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Notes: Projection microradiography was used to determine the density and orientation of the force transmitting structures, i.e., trabeculae and bone lying between approximately parallel vascular canals, within the bones of cat skulls. The organisation in the skulls was confirmed statistically for a total of ten cats. The results of the observations showed that within specific areas of the skull a high degree of structural orientation and an increased density of osseous structures was present. The distribution of these characters corresponded in contiguous bones such that a continuum of structural organisation was established between the alveolar region and the site of attachment of the temporalis and masseter muscles and the glenoid region.The patterns of force transmission during jaw closure were determined when a resistance was placed initially between the canines and then the carnassials. An analysis was first carried out on dry skulls using colophonium resin to determine the direction of the force distribution. The nature and the approximate magnitude of the forces were ascertained by replacing the resin with strain gauges. The basic similarities in the strain patterns recorded from the dry skulls and those from the ten anaesthetised cats in which strain gauges had been intra-vitally implanted, substantiated the recordings made on the dry skulls. Combination of the results from the three sets of experiments defined the patterns of force distribution in the cat skull during the closure of the mandible against a resistance. The results showed that: (1) the combined action of the temporalis and masseter muscles tended to reduce the overall strain in the skull bones, and that the deformations produced by the action of the masseter were greater than that exerted by the temporalis muscles; (2) during biting, whether the resistance was placed between the canines or carnassials, compressive forces predominated in the facial bones; (3) small movements observed between facial bones indicated the presence of a flexible component within the skull, thus allowing large forces to be exerted during biting without overstressing the facial bones; (4) the glenoid fossa is part of a force bearing joint; (5) forces generated during biting were resisted within the skull by forces of an opposite nature generated within the system, the incompressible nature of bone and by the effect of the soft tissues; (6) the nature and the magnitude of the strain altered when a resistance was placed at the canines and then at the carnassials; however, the pattern of force distribution within the skull remained the same; (7) there was a direct correspondence between the detailed structural organisation of the bones and the patterns of force distribution. This conclusion would appear to apply in general to mammalian skulls. The study also emphasises the importance, neglected hitherto, of carrying out a variety of experiments to determine the patterns of force distribution in bones.The Trajectorial Theory of bone organisation is discussed and, on the basis of the results obtained, a modified theory is proposed. This states that: the structural continuum is common to the compact and cancellous bone and comprises bony bars which are aligned in the optimum direction for the transmission of force to a region in the bone or bones where it is effectively resisted.

Notes: The tarsi of all three pairs of legs of both sexes of Aedes aegypti (L.) bear spine sensilla, five types of hair sensilla, which are designated A, B, C1, C2 and C3, and campaniform sensilla. Type A and B hairs, spines, and cam-paniform sensilla are innervated by one neuron with a tubular body, a characteristic of cuticular mechanoreceptors. In particular the hairs and spines are tactile receptors and the campaniform sensilla are proprioceptors. The C1, C2, and C3 hair sensilla have the morphological features of contact chemoreceptors. Type C1 and C3 hairs are innervated by five and four neurons, respectively, which extend to the tip of the hair. Type C2 is innervated by five neurons, one of which terminates at the base of the hair in a tubular body while the remaining four extend to the tip of the hair. The role of the type C hairs in oviposition behavior, nectar feeding, and recognition of conspecific females is discussed. Presumed efferent neurosecretory fibers occur near the spine and hair sensilla.

Notes: The micro-anatomy of the corpuscles of Stannius of the toadfish, Opsanus tau, an aglomerular marine teleost, has been studied by light and electron microscopy. The corpuscles are composed of extensively anastomosed cords of epithelial cells which maintain intimate contact with blood capillaries. Most of the epithelial cells contain acidophilic granules which also show a positive reaction with the periodic acid-Schiff technique and aldehyde fuchsin. On the basis of fine structural criteria, three cell types can be recognized. The granular cells contain abundant quantities of granular endoplasmic reticulum, ribosomes, Golgi apparatus with prosecretory granules, coated vesicles, polymorphic mitochondria with lamellar cristae, filaments, microtubules, a cilium, a variety of lysosome-like dense bodies, glycogen particles, lipid droplets, secretory granules and intranuclear lipid-like inclusions. One variety of agranular cell (type I) is characterized by the total absence of secretory granules, but it contains large amounts of granular endoplasmic reticulum and ribosomes, conspicuous profiles of Golgi apparatus, coated vesicles and sometimes an abundance of glycogen. Another variety of agranular cell (type II) has poorly developed cytoplasmic organelles. The perivascular space between the capillary and parenchyma contains connective tissue cells and abundant nerve fibers. The different types of epithelial cells observed in the corpuscles of Stannius of this fish may represent functional stages of the secretory cycle in a single cell type.

Notes: The nervous system of the maldanid polychaetes Clymenella torquata (Leidy) and Euclymene oerstedi (Claparede) (= Caesicirrus neglectus [Arwidsson, '11-'12]) retains its primitive association with the epidermis. It shows only slight metamerism in the presence of larger collections of neurones opposite the parapodia and of larger nerves at the segmental boundaries. Multicellular giant fibers are present in the ventral nerve cord; giant neurones which show a characteristic pattern of distribution in each species are also present. The cerebral ganglia supply nerves to the prostomial wall, nuchal grooves and the wall of the buccal cavity, and a pair of large nerves from the circumpharyngeal connectives also appear to join the buccal system. The organs of special sense are the elongated prostomial nuchal grooves, and prostomial ocelli in Euclymene but not in Clymenella. Statocysts are absent.Four pairs of nephromixia are present. They lie in the aseptate anterior trunk, in chaetigers 5-9 of Clymenella, and 6-10 of Euclymene. The nephridiopores lie at the ventral ends of the neuropodia of chaetigers 6-9 and 7-10, respectively. Each nephromixium consists of coelomostome, tubule and contractile bladder. The wall of the tubule and bladder consists of both excretory and ciliated cells. Most of the cytoplasm of the latter forms a bounding layer at the outer surface. The cytoplasm of the excretory cells contains lipid material and appears to synthesize lipofuscin. The tips of the excretory cells swell, fill with granules, and break off in the form of vesicles which are periodically expelled in clouds from the nephridiopores. Glycogen is present, especially in the ciliated cells of the tubule and coelomostome.Granules of a lipoid nature accumulate in (or between) cells of the nephridia, epidermis, and some regions of the gut, and may be excretory. Lipid granules also appear to be synthesized by coelomocytes which eventually end up in masses in the ventrolateral coelomic cavities of the tail.The nephridia act as gonoducts, but show no seasonal variation in either size or histological structure.

Notes: The ascophoran Pentapora foliacea was studied from epoxy sections of skeletal and soft (hard-soft) tissues. The basal wall is double, indicating the colony grew as two independent layers, back to back. The structure of the vertical walls and interzooidal communication organs indicates that zooids were budded in the usual way as in most encrusting cheilostomes. Secondary layers of the frontal wall are of acicular aragonite. The ovicell develops as a flattened cuticular bladder in early ontogeny; the aragonitic layer of the frontal wall later engulfs it. A median vesicle, an evagination of the vestibular wall, is present but the eggs may be supplied with sufficient yolk to nurture the embryo. The overall ovicell structure is similar to that of hyperstomial ovicells in other cheilostomes.

Notes: This investigation describes the pre-natal morphogenesis of the type I pneumocyte subsequent to its differentiation from pulmonary epithelium. Cells lining subpleural alveolar septa were photographed from serial sections with the electron microscope, and a three-dimensional representation of each cell was obtained by transferring the contours of the cell membranes from montages to transparent plastic sheets which were then spaced to scale and stacked. The results of this study indicate that: The nascent blood-air barrier of a 50-day reconstructed cell was twice as thick as the average definitive barrier; definitive barrier thickness was observed in some areas in a 63-day reconstructed cell; the amorphous component of elastic tissue which appears peripherally in septal connective tissue during pre-natal morphogenesis may be directly juxtaposed to the basal lamina of the alveolar epithelium; the orientation of the cell junction between a pneumocyte and its neighboring cells, as observed in sections of alveolar septa, changes as the contour of the pneumocyte changes from simple abutment to overlapping patterns.

Notes: The fine structure of the mid-gut musculature of the desert locust, Schistocerca gregaria is described and compared with that of the visceral muscles of other species. The gross morphology and fine structure of the nervous system which supplies the mid-gut muscle fibres is described.

Notes: The integument of Paranthessius anemoniae has been studied with light and electron microscopy. A cuticle with clearly defined epicuticular, exocuticular and endocuticular regions overlies a cellular hypodermal layer. The distribution of carbohydrate, lipid and protein components of the cuticle were demonstrated histochemically. Parabolic striations in oblique sections of cuticle suggest that its molecular architecture fits a “twisted sheet” theory proposed for other species.Arthrodial membranes at body and limb joints have a homogeneous structure, lacking exocuticle and endocuticle. Subcuticular glands appear to secrete substances thought to be responsible for the immunity which Paranthessius seems to have to the nematocysts of its host. Small hairs, situated in cuticular cups which occur over the dorsal body surface are considered to function as rheoreceptors.

Notes: The larval epithelium of the sea urchin, Lytechinus pictus, consists of squamous cells and bands of columnar epithelial cells bearing cilia. During metamorphosis this tissue undergoes a series of rapid, complex changes. Through the scanning and transmission electron microscope, we describe and analyse these changes. The changes can be divided into three steps. (1) The larval arms bend away from the left side of the larva, exposing the urchin rudiment. Cells which are identical to smooth muscle cells are in a position to bring about this bending. (2) The squamous epithelial cells assume a cuboidal shape. This change in shape results in the collapse of the larval epithelium onto the presumptive aboral surface. These cells possess a subapical band of microfilaments. The cellular shape change but not the bending of the arms is reversibly inhibited by Cytochalasin B. These observations suggest a mechanism for this change. (3) The former lining of the vestibule of the urchin rudiment comes to lie over the collapsed larval tissue and forms the adult epithelium. At this point, after only one hour, the larva has assumed the external shape of an adult sea urchin.

Notes: The mucous gland of the red-spotted newt, Notophthalamus viridescens viridescens, Rafinesque was examined by histochemical and ultrastructural techniques and its cytological responses to various hormonal conditions were studied. Its secretory epithelial cells produce and release in merocrine fashion a neutral, unsulphated mucosubstance. The secretory epithelium is bounded peripherally by a thin, but apparent non-functional, myo-epithelium. The duct of this mucous gland consists of a single keratinized tubular cell that extends from the neck region of the gland to the surface of the epidermis.Mucous secretion is absent or greatly reduced on the skins of newts maintained under laboratory conditions for a few weeks but reappears after injection of ovine prolactin. Mucous glands in laboratory conditioned animals show a 4-fold increase in volume brought about by the engorgement of their epithelial cells with secretory granules. Ovine prolactin reduces the volume of the glands to unconditioned levels with a corresponding reduction in granular content, suggesting that prolactin functions in the release of the granules. This view is reinforced by the findings that autotransplantation of the pituitary gland prevents the conditioning effect and that glandular volume increases in auto-transplanted animals given ergocornine. Granular accumulation begins also in hypophysectomized newts but ceases after a week, indicating the need for some hypophyseal factor in the synthesis as well as the release of the granules. Ovine prolactin restores mucous glands of hypophysectomized newts to the unconditioned state. Contrary to earlier findings, ovine prolactin induces a reduction in the volume of the mucous gland in thyroidectomized newts.

Notes: The process of coelomic pouch formation in Pisaster ochraceus was studied with light microscopy, transmission and scanning electron microscopy and time-lapse cinemicrography as well as with the drug cytochalasin B. As in most asteroids, the paired coelomic pouches of Pisaster ochraceus are formed from outpocketing of the archenteron.Arrays of 50 Å microfilaments are found in the presumptive coelomic pouch cells at the apex of the archenteron as well as in the filopodia of the mesenchyme cells. Both cell types undergo active movements throughout the entire process. Treatment of embryos with cytochalasin B (CCB) during coelomic pouch formation results in the loss of cell movements and the regression of the coelomic pouches; this is accompanied by the loss of microfilament arrays in both cell types. Cell movements and microfilament arrays reappear on removal of CCB and coelomic pouch formation resumes.Our evidence suggests that the microfilaments in the presumptive coelomic pouch cells provide the main force for the outpocketing movement. The major role of the microfilament arrays in the filopodia of the mesenchyme cells associated with the coelomic pouches is to determine the definitive shape and location of the pouches.

Notes: Morphological changes of the ovary of the Chinese cobra, Naja naja, throughout the annual reproductive cycle are described. A single clutch of between 6 and 22 eggs is produced in late June. From July to the following April the ovary remains quiescent and contains small previtellogenic, hydration stage follicles. The growth of an ovarian follicle from a primary oocyte to maturation and ovulation is estimated to take three years. The histology of the germinal epithelium and the follicular granulosa shows seasonal changes correlated with the growth of the oocyte. During the quiescent period, the germinal epithelium lacks mitotic activity, but during April, when yolk deposition and rapid growth of the preovulatory follicles take place, the germinal epithelium shows intense mitotic activity. The growth of the smallest hydration stage follicles, and the occurrence of cytoplasmic bridges between the pyriform cells of the granulosa and the developing oocyte, also appear to increase during this period. The possible function of the pyriform cell is discussed and the literature on the origin and fate of these cells in the squamate ovary is reviewed. Postovulatory follicles (corpora lutea) and two types of atresia are described and compared with what is known of these structures in other reptiles.

Notes: An experiment was undertaken to determine which sensory structures of the mouse embryo inner ear developed from what portion of the mouse otocyst. Otocysts of gestation days 10, 11, 12 and 13 were divided by surgical dissection into six anatomical groups: dorsal, ventral, anterior, posterior, medial and lateral halves. They were organ cultured separately. After a period of ten days, the explanted tissues were harvested and processed histologically for microscopic analysis. The surgical control specimens fixed at the time of explanation were composed of undifferentiated ectodermal cells for tissues of gestation days 10, 11, and 12. Otocysts of gestation day ten showed no gross morphological differentiation. Otocysts of gestation days 11 and 12 showed, during the course of their subsequent growth, that the three semicircular ducts and their associated cristae developed from the dorsal and lateral halves. Only the anterior and posterior canals and cristae originated from the medial portion. The posterior half gave rise to the posterior crista and the anterior half provided for the development of the anterior and lateral cristae. The cochlear duct and its sensory epithelium developed in all the anatomical groups except the dorsal half. The utricle developed in the dorsal section of the middle third of the otocyst, while the utricular macula developed in the anterior half of the same section of the otocyst. The saccule and its macula differentiated from the ventral section of the middle third of the anterior half.

Notes: The pineal-paraphyseal complex of sea turtles is an impressively large structure which projects dorsally and anteriorly above the prosencephalon. The complex was examined by light microscopy in several age classes of green sea turtles (Chelonia mydas) and from juvenile loggerhead turtles (Caretta caretta). The paraphysis is extensively fused to the distal portion of the pineal body, suggesting an interrelated function for these two tissues. No duct or canal was observed connecting the pineal lumen to the third ventricle. Two pineal cell types are described which appear to correspond to the neuroglial supportive cells and the secretory rudimentary photoreceptor cells of other amniotic vertebrates. A possible luminal secretion in the form of apical protrusions is produced by the latter cell type. No typical photoreceptive outer segments were observed.

Notes: The fine structure of the wax gland of Anomoneura nymph and its metamorphic change were investigated. In the nymph, this organ encircles the anus, and consists of two kinds of cells, derived from epidermal cells: (1) very tall, slim wax cells, which produce and secrete the wax, and (2) flat interstitial cells found among the wax cells. The whole gland is covered by a wax-secreting cuticle with a delicate surface sculpture. Each wax cell has a long, wide duct which opens at the cuticle and penetrates the entire cell. Its cytoplasm is rich in mitochondria and smooth endoplasmic reticulum while that of interstitial cells contains rough endoplasmic reticulum. During each nymphal molt, the cluster of primordial wax gland cells  -  derived from the epidermis  -  proliferates rapidly and forms the gland of the next instar. The gland of the preceding instar meanwhile degenerates. Interstitial cells play an important role in cuticle formation and shedding at each molt. These cells alone produce and deposit the new cuticle of the next instar; the wax cells, specialized for wax production, cannot produce cuticle. The apical portion of the wax cell is cut off from the main cell body by growth of the surrounding interstitial cells. Thereafter, the wax cells degenerate, resulting in the rapid disappearance of the previous instar's wax gland. Adults lack this gland entirely.

Notes: The dorsal ventricular ridge (DVR) is a subcortical, telencephalic structure in reptiles and birds that protrudes into the lateral ventricle. The structure of DVR has been studied in the red-eared turtle (Pseudemys scripta elegans) in Nissl and Golgi preparations. The DVR in Pseudemys is divided into the anterior dorsal ventricular ridge (ADVR) and the basal dorsal ventricular ridge (BDVR) by the dorsal branch of the middle ventricular sulcus. The structure of ADVR has been examined in detail.The ADVR is divided into four regions with distinct boundaries termed dorsal area, medial area, ventral area and central area. Dorsal area, medial area and ventral area border on the lateral ventricle; central area lies deep to the other areas. Three classes of neurons are found in Golgi preparations of ADVR. Juxtaependymal cells have somata near the perikarya of ependymal cells; their dendrites are found primarily in a periventricular fiber zone. Aspiny neurons were observed only in the dorsal half of ADVR and appear to be restricted to deep regions of the ridge. These multipolar neurons are rarely encountered in Golgi preparations, and the observed distribution may not represent their actual distribution in ADVR. The majority of the cells observed in ADVR are spiny neurons with dendritic fields that range from stellate to double-pyramidal. Cells in this class may be subdivided on the basis of axonal morphology into at least two groups, but further studies are needed to determine the range of axonal morphology exhibited by these neurons.An analysis of the distribution of these cell types in Golgi material shows that dorsal area, medial area and ventral area are organized in four zones concentric with the ventricular surface. Central area apparently lacks a concentric pattern of organization. Zone 1 is a periventricular fiber band that contains juxtaependymal neurons and ascending dendrites of zone 2 spiny neurons, and it may serve as a structural substrate for segregated input onto these cell populations. Zone 2 contains clusters of spiny neurons with apposed somata, which vary in size and distribution between areas. Dendrites of zone 4 neurons are also found in the deep half of zone 2. Zone 3 is a cell-poor region which lies at the center of a region of overlapping dendritic fields of zone 2 and zone 4 neurons. Zone 4 contains predominantly spiny neurons (aspiny neurons are found only in the dorsal half of ADVR) which are either isolated or in small clusters with apposed somata. Dendrites of zone 2 cells extend superficially into zone 4, so that the deep portions of zone 4 may be a substrate for segregated input to zone 4 neurons. These zones are differentially elaborated in each area. Central area, by contrast, consists of scattered spiny and aspiny neurons among fibers connecting ADVR and the lateral forebrain bundle.A comparison of these findings with the ADVR of snakes (Ulinski, '78a,b) shows both similarities and differences in DVR organization in the two taxa. Although snakes lack areal divisions, ADVR is organized in four concentric zones (zones A-D). Zones A and B resemble zones 1 and 2 in turtles, consisting of a superficial fiber zone and a subjacent cell cluster zone. The clusters are smaller in snakes than in turtles. However, snakes lack a cell-poor band deep to zone B, and dendrites of cells in zone C enter zone A. Thus, there are differences in both areal and zonal dimensions of ADVR organization in turtles and snakes.

Notes: Ultrathin sections of the nasal barbel of the channel catfish, Ictalurus punctatus, were studied in the electron microscope and the fine structure was compared to that of barbels of other teleosts and to the mandibular (dentary) barbels of I. punctatus. While the overall histology of the nasal barbel is similar to that of barbels described previously, this study revealed far greater cellular complexity and variability than was previously reported. A layer of stratified epidermal cells rests upon a connective tissue dermis containing a cartilage rod, a large number of nerve fibers and numerous blood vessels, fibroblasts and pigment cells. Taste buds are present in the epidermal layer. This layer was found to contain probably 16 kinds of cell types, several of which may represent transitional stages, in addition to taste bud cells. Observations were made pertaining to innervation and cell types in the taste buds. A new terminology for designating the barbels of I. punctatus is suggested.

Notes: New data on the brain of Latimeria indicate that previous estimates of the brain weight were too high by a factor of two. Our data suggest a brain weight of 1.1-1.5 grams for a specimen with a body weight of 30 kilograms. Quantitative data on major divisions of the brain are presented for the first time, and the relative size of the major brain divisions is similar to that of sturgeons and generalized sharks (such as hexanchids and squalids). Examination of brain component weight (s): body weight plots in a sample of non-teleost actinopterygian fishes indicates that all major divisions of the brain, except the telencephalon, are larger than in Latimeria. Brain component sizes in Latimeria are more similar to those extrapolated for amphibian brains than to those for actinopterygians. However, the cerebellum of Latimeria is considerably larger than that of amphibians.

Notes: The Champy-Maillet osmium tetroxide-zinc iodide technique and a new method using azur B-sodium thioglycolate were used to study the general nervous tissue structure in planarians. A subepidermal and a submuscular nerve plexus, partially reported by earlier authors, are described, and a gastrodermal plexus is reported for the first time in triclads. The possible functions for each one of these plexuses are discussed. By the Champy-Maillet method, the innervation within the parenchyma appears as an array of numerous single nerve fibers that course between the parenchyma cells making apparent synaptic contacts. The pharynx has outer and inner nerve nets similar in structure to the submuscular nerve plexus. Both nerve nets are connected to each other by radial nerves.The central nervous system has a sponge-like structure with many lacunae filled with cell bodies, dorso-ventral muscle fibers, parenchymal cell processes and excretory ducts. The existence of this sponge-like nervous tissue structure is discussed in relation to the still incomplete centralization of the nervous tissue in these organisms, to the lack of a true vascular system and to the acoelomate level of organization. A comparison with the nervous tissue structure of more advanced groups like polyclads and nemertines is suggested.

Notes: Secretion in the salivary glands of Gromphadorhina portentosa involves three cell types: parietal cells, secretory cells, and duct cells. The organization and role of the parietal and secretory cells are here considered. Parietal cells have numerous mitochondria, indicating an active metabolic role and the subsequent production of ATP. Plasma membrane invaginations and intracellular ductules containing microvilli appear to function in the absorption of solutes from the hemolymph and finely-tapered ductules. Secretory cells contain abundant rough endoplasmic reticulum, the three forms (stacked, vesicular, and diffuse) of which appear to develop sequentially during maturation. Secretory vesicle formation is asynchronous between adjacent secretory cells, and apparently the large vesicles often coalesce. The secretory vesicles also show differing degrees of electron density, indicating distinct biochemical composition.

Notes: Studies were undertaken of the microcirculation and histology of the gill of Protopterus aethiopicus as a prerequisite for elucidating the function of the gills in a bimodal respiratory system. The lamellae of the gill-bearing arches (I, IV, V, VI) resembles the arborescent external gill of the larval amphibian rather than the gill of the teleost or selachian.The arterio-arterial system (a-a) of the gill consists of an afferent artery, a series of large capillaries, and an efferent artery on each of the primary, secondary and tertiary lamellae. There are no pillar cells and the loose capillaries are covered with a multilayered epithelium. While living in water, the minimum distance for gas exchange is of the order of 5 μ. An afferent-efferent arterial shunt at the base of each primary lamella may be involved in control of lamellar blood flow and the resistance of the gill vasculature.The arterio-venous system originates primarily from the efferent side of the arterio-arterial system and drains into large branchial veins. Numerous contractile cisternae, interposed between intercellular channels and veins, presumably function as micropumps that collect fluid from intercellular epithelial spaces and inject it into the venous circulation.During aestivation, the epithelial layer of the gill lamellae becomes thinner. The entire gill vasculature, including the capillaries and afferent-efferent shunts on arches IV-VI, are very dilated which presumably promotes blood flow through these gill arches to the lungs.

Notes: The movements of the shoulder girdle of eight adult cats during overground stepping were studied, using standard slow motion cinematographic techniques. The patterns of activity of shoulder muscles were examined, using simultaneous intramuscular electromyography. Walking, trotting and galloping steps were analyzed from digitized single motion picture frame images. Angular movements of the shoulder girdle consist of biphasic flexion and extension of the shoulder joint and a monophasic flexion-extension alternation of the scapula on the thorax during each step cycle. In addition, the center of the scapula moves craniad during the swing phase and caudad during the stance phase with respect to a fixed reference point on the animal. Similar vertical movements of the center of the scapula also occur in each step cycle. Results of EMG studies of the 17 muscles capable of acting on the shoulder girdle indicate that three overall patterns of activity are found: (1) a pattern typical of extensor muscles, active during all the extension epochs; (2) a pattern typical of flexor muscles, active during the flexion epoch; and (3) a biphasic pattern of activity, active twice in each step. These data are used, along with a re-examination of previous models of the mechanics of the shoulder girdle of carnivores to examine the function and mechanics of shoulder motion. It is concluded that the rotary and translatory movements of the shoulder girdle during stepping combine to enhance step length.

Notes: The most striking morphological feature of the ovarian epithelium of Cymatogaster is the presence of intercellular dilations during much of the year. These dilations increase markedly in volume during the several months prior to ovulation and fertilization, and decrease in volume during the months of embryogenesis and gestation. The epithelium then returns to its initial, relatively undifferentiated state. The extracellular material within the dilations likely is synthesized in the cells adjacent to or within the dilations. Apparently most of this material is released into the ovarian lumen when the apicolateral margins of adjacent epithelial cells pull apart; possibly it serves as nutrient for developing embryos.In addition to supporting embryogenesis, the ovarian epithelium also apparently is involved in sperm storage. Sperm are maintained within pockets in the ovarian epithelium for the several months between insemination and fertilization. The cells lining the sperm pocket do not develop the intercellular dilations characteristic of most of the ovarian epithelium, and sperm remain associated only with the sperm pocket cells.

Notes: The antennae of Folsomia candida and Hypogastrura copiosa are provided with tactile hairs on all four segments and, in addition, with chemoreceptors on segments three and four. The cuticle of the thin-walled chemo-receptors of Folsomia, as in most other insects, is penetrated by many small pores uniformly distributed over the surface. In contrast, the cuticle of the thin-walled chemoreceptors of Hypogastrura is unusual in that a band of cuticle without perforations spirals around, or partly around, the hair. The cuticle between the spirals is very thin, and has extremely small openings in it. The tip of the antenna of Folsomia is thin, permeable to dyes in aqueous solution and apparently glandular. The antennal tip of Hypogastrura is definitely glandular.

Notes: After hemisection of the spinal cord and medulla oblongata, a projection has been traced to the inner half of the tectal white of the tiger salamander, using Fink-Heimer degeneration staining. By microelectrode recording it was found that the tectal projection forms a topographic somatosensory map of the contralateral half of the body. This map is in register with the overlying retino-tectal visual projection. Using the Falck-Hillarp technique, it was found that the somatosensory tectal input is associated with yellow-fluorescing 5-hydroxytryptamine fibers.

Notes: A comparative morphological study concerning typology and topography of chemoreceptors on the prothoracic legs of Calliphora vicina, Phormia terranovae and Musca domestica has been carried out. The typological criteria of Grabowski and Dethier ('54) and Hansen and Heumann ('71) were used. A single criterion, the shape of the tip, was used to define the different types of chemoreceptors.A-hairs have a rhombic pore at the side of the tip; B-hairs have an oval pore at the tip apex and D-hairs have a rectangular pore under an undulated, cap-like structure at the hair tip. A-, B-and D-hairs were found in the tarsomeres of Phormia; in Musca and Calliphora only B- and D-hairs were found. An opening and closing mechanism may operate on the pores of the tips of the chemoreceptors. Chemoreceptors were counted and a topographical map was completed, using SEM-techniques. Topographical maps are of value in electrophysiological and behavioural research, where only a limited optical magnification is possible.

Notes: The structures of the lantern tracheoles of three genera of flashing fireflies are compared. All three genera have stiff, reinforced tracheoles which resist folding or collapsing under conditions which flatten more typical tracheoles. This common specialization supports the hypothesis that the tracheoles play a major role in flash control in these fireflies, especially as the morphological basis of the stiffening is different in the three genera. Study of the tracheoles of other tissues reveals that there is great variety in structure and flexibility of these vessels from tissue to tissue and organism to organism, suggesting that tracheolar specialization may be a general phenomenon, with the fine structure of these air tubes being tailored to the particular demands and conditions of the tissues in which they are found.

Notes: Tibiotarsal segments of 12-day chick embryos homozygous for the crooked neck dwarf gene (cn/cn) were examined histologically following routine methods of preparation. The myogenic mass fails to divide into separate muscle bundles during the early stages of differentiation. Myoblasts and myotubes are observed, although the proportion favors the mononucleate cell population. Multinucleate myotubes are often wavy in appearance and many contain eosinophilic cytoplasmic inclusions. The entire tissue mass of mutants appears more compacted than in control limbs. Poor organization of muscle appears related to the lack of a suitable connective tissue system. Epimysia, perimysia, and subcutaneous connective tissue fail to develop properly. Tendons are poorly developed or absent. Comparisons between mutant and control embryos show no differences in peripheral innervation. Nerve fascicles penetrate deeply into the developing muscle of both species. The distribution of vascular elements is seemingly normal also. Skeletal muscle of cn/cn embryos is capable of differentiating to the myotube stage, after which it undergoes cellular degeneration without achieving a functional state. Comparisons of this mutant with alleged chemical phenocopies show important differences.

Notes: The histology and carbohydrate histochemistry of eight teleostean stomachs are compared. Three gross anatomical types of stomachs are described and their shapes appear to correlate somewhat with feeding habits. Each type can be divided histologically into a corpus and pylorus. Gastric glands, containing only one cell type, occur in the copora of all species, but are present in the pylori of esocids only. As a single cell can produce both enzymes and hydrochloric acid such cells may be comparable to those of amphibians but not mammals. Lamina propria and submucosa are indistinctly separated in corpora but better defined in pylori by an intervening muscularis mucosa. The arrangement of the muscularis into inner circular and outer longitudinal layers is the opposite of that seen in the esophagus. Gastric mucous cells show species variations in localization of epithelial mucosubstances, which in broad terms are recognized as sulfomucins, sialomucins and neutral mucosubstances. A piscivorous diet does not appear to demand any particular type of carbohydrate. Within the Centrarchidae, gastric pit cells vary in carbohydrate content from only neutral mucosubstance to only weakly acidic sulfomucin; two species contain both types. A positive PAS reaction on the surface of gastric epithelial cells is suggestive of a striated border and thus possibly absorptive function. The absence of stomachs in some teleosts and the evolutionary and dietary significances are discussed.

Notes: The American cockroach has a total of 368 muscles inserting on the post-coxal segments of its legs. By using a narrow morphological definition for delimiting individual muscles, it is shown (i) that the protrochanteral musculatures (23 muscles/leg) differ from the essentially identical meso- and metatrochanteral musculatures (24 and 26 muscles/leg) in number and disposition of extensors and in having a completely different flexor composition, and (ii) that the musculatures of the more distal segments of the legs are completely serially homologous, there being 2 muscles for moving each femur, 23 for each tibia, 7 for each first tarsomere, and 5 for each of the paired pretarsal claws. In all six legs, the trochanteral and tibial musculatures each contain single slender muscles that may be acting proprioceptively to measure the angular displacements between, respectively, the coxas and trochanters, and the femurs and tibias. Neurological and phylogenetic considerations are used to demonstrate why a narrow morphological definition should be employed, and why the widely used functional definition of Snodgrass ('35) is not only fallacious on evolutionary grounds, but also leads to making erroneous conclusions regarding the manner in which insect musculature is controlled by the insect central nervous system. Finally, it is hypothesized that the physiological limitations imposed by having an open circulatory system and the problems inherent in the neural control of large muscles may have been major evolutionary factors in forcing insects to use many slender muscles to control their body movements.

Notes: Among piscivorous cichlids consistent differences have been recorded between ambush and pursuit hunters with respect to electromyographic, kinematic, pressure and behavioral profiles during prey capture by high speed inertial suction. Piscivorous cichlids possess a repertoire of at least two patterns of prey capture, each of which is characterized by an extreme regularity of the kinematic, pressure, electromyographic and behavioral profiles. The nature and locomotory behavior of the prey, visually analyzed by the predator during the prestrike stalk, determine which of the two preprogrammed patterns is recruited. Agile and elusive prey invariably will elicit a preprogrammed motor output (stereotyped motor pattern) that produces the greatest suction velocities in both ambush and pursuit hunters. The greater the kinematic and suction velocities, the greater the overlap of the firing sequences of antagonistic muscle complexes. The opercular and branchiostegal apparati function as an exceedingly effective anti-backwash device, damping potential fluid oscillations within the oropharynx. Mastication occurs by triphasic movements and actions of muscles of the upper and lower pharyngeal jaws in both ambush and pursuit hunters. The lower pharyngeal jaw is acted upon by a force couple of which the fourth levator externus on one hand and the pharyngocleithralis externus and pharyngohyoideus on the other hand are the antagonistic components. Furthermore, the lower pharyngeal jaw is suspended by a muscular sling, the tension of which can be modified continuously. It is postulated that the switch from insectivorous to piscivorous feeding regimes (and perhaps vice versa) is accomplished by very minor structural and functional modifications, because the modulatory multiplicity and total range of repertories of the feeding machinery of the two trophic groups overlap significantly. Piscivorous cichlids may not have arisen by orthoselection in gradually-changing lineages, but represent the differential success of subsets from a random pool of speciation events. Adaptive features identified as characteristic for piscivory could have evolved in multiple and independent lineages at a punctuational mode and tempo.

Notes: There are two discrete lobes comprising the armadillo subman-dibular gland. These two lobes can be defined grossly, histochemically and morphologically with the light and electron microscope. The minor lobe stains more intensely with PAS and AB. When viewed in the electron microscope, the secretory granules of the acinar cells within this lobe appear mucous-like. The granules of the demilune cells are slightly different in appearance. The secretory granules of the acinar cells in the major lobe contain many dense foci embedded in a fibrillar matrix, a substructure not described previously. The demilune cells of this lobe contain secretory granules with a mucous-like structure which is consistent throughout the entire lobe. As in the minor lobe, these demilune cells stain very intensely with PAS and AB.

Notes: End-plate distributions have been determined for three frog muscles of different morphology in order to relate end-plate topography to spatial muscle structure and nerve branching. Koelle's cholinesterase technique was applied, both on whole muscles and frozen sections. The end-plates of the short parallel-fibered cutaneus pectoris muscle appeared to be located in short bands along the nerve branches. The nerve tree is restricted to a zonal area across the middle part of the muscle. Depending on the way the nerve branches, the end-plate bands form innervation patterns, varying from one single continuous band to multiple distributed bands. In the latter case one frequently observes that different end-plate bands do not run across the same longitudinal muscle fiber area, although the respective nerve branches run parallel across this area. The long parallel-fibered sartorius muscle has a wider nerve tree and exhibits the same phenomenon for close parallel nerve branches, but end-plate bands along parallel nerve branches far apart cover the same muscle fiber area. The end-plate distribution in the bipennate, short-fibered gastrocnemius is zonal throughout the muscle except in certain compartments containing tonic fibers. The end-plate zone centers around the inner aponeurosis about half-way between the muscle tendon junctions of the fibers and is visible only at the muscle surface where muscle fibers run over their entire length at that surface. The results are of general use in the electrophysiology of neuromuscular transmission because they illustrate how in certain twitch muscles neuromuscular morphology may help to localize end-plates.

Notes: When a larva of Haplothrips verbasci is ready to feed, it grasps the surface of the leaf with its pretarsi, sinks down between its front legs, lifts its head, and places the tip of its mouthcone against the surface. It then shortens its mouthcone and punches a hole in the epidermis by rapidly and repeatedly protracting and retracting its left mandibular stylet. The thrips then inserts its two maxillary stylets as a unit into the wound with a series of rapid thrusts and withdrawals, salivating continuously while doing so. When a food source in the epidermis or mesophyll is found, probing and salivation stop and cibarial pumping begins. Cytoplasm is sucked into the opening at the tip of the protracted stylets, up the food canal between them and into the cibarium.Probing and feeding can occur without mandibular intervention but uptake of liquid seems to require use of the mutually coadapted maxillary stylets, even when these are fully retracted.Prior to molting, the larva protracts its maxillary stylets maximally and, in the pharate state, seems incapable of feeding or drinking.Structures used in feeding are fully described and are shown to resemble those of Hemiptera except for the presence of maxillary and labial palpi and the absence of the loral lobes, right mandible and of a salivary canal between the protracted maxillary stylets. Seven single and 18 paired muscles function in the feeding act, nine less than in adults of the same species.Differences in the feeding mechanism of terebrantian and tubuliferous thrips are discussed and evidence is presented to suggest that the simplified and more highly specialized mouthparts of the latter insects are adaptations for feeding in confining spaces.

Notes: In contemporary entomology the morphological characters of insects are not always treated according to their phylogenetic rank. Fossil evidence often gives clues for different interpretations. All primitive Paleozoic pterygote nymphs are now known to have had articulated, freely movable wings reinforced by tubular veins. This suggests that the wings of early Pterygota were engaged in flapping movements, that the immobilized, fixed, veinless wing pads of Recent nymphs have resulted from a later adaptation affecting only juveniles, and that the paranotal theory of wing origin is not valid. The wings of Paleozoic nymphs were curved backwards in Paleoptera and were flexed backwards at will in Neoptera, in both to reduce resistance during forward movement. Therefore, the fixed oblique-backwards position of wing pads in all modern nymphs is secondary and is not homologous in Paleoptera and Neoptera. Primitive Paleozoic nymphs had articulated and movable prothoracic wings which became in some modern insects transformed into prothoracic lobes and shields. The nine pairs of abdominal gillplates of Paleozoic mayfly nymphs have a venation pattern, position, and development comparable to that in thoracic wings, to which they are serially homologous. Vestigial equivalents of wings and legs were present in the abdomen of all primitive Paleoptera and primitive Neoptera. The ontogenetic development of Paleozoic nymphs was confluent, with many nymphal and subimaginal instars, and the metamorphic instar was missing. The metamorphic instar originated by the merging together of several instars of old nymphs; it occurred in most orders only after the Paleozoic, separately and in parallel in all modern major lineages (at least twice in Paleoptera, in Ephemeroptera and Odonata; separately in hemipteroid, blattoid, orthopteroid, and plecopteroid lineages of exopterygote Neoptera; and once only in Endopterygota). Endopterygota evolved from ametabolous, not from hemimetabolous, exopterygote Neoptera.The full primitive wing venation consists of six symmetrical pairs of veins; in each pair, the first branch is always convex and the second always concave; therefore costa, subcosta, radius, media, cubitus, and anal are all primitively composed of two separate branches. Each pair arises from a single veinal base formed from a sclerotized blood sinus. In the most primitive wings the circulatory system was as follows: the costa did not encircle the wing, the axillary cord was missing, and the blood pulsed in and out of each of the six primary, convex-concave vein pair systems through the six basal blood sinuses. This type of circulation is found as an archaic feature in modern mayflies. Wing corrugation first appeared in preflight wings, and hence is considered primitive for early (paleopterous) Pterygota. Somewhat leveled corrugation of the central wing veins is primitive for Neoptera. Leveled corrugation in some modern Ephemeroptera, as well as accentuated corrugation in higher Neoptera, are both derived characters. The wing tracheation of Recent Ephemeroptera is not fully homologous to that of other insects and represents a more primitive, segmental stage of tracheal system.Morphology of an ancient articular region in Palaeodictyoptera shows that the primitive pterygote wing hinge in its simplest form was straight and composed of two separate but adjoining morphological units: the tergal, formed by the tegula and axillaries; and the alar, formed by six sclerotized blood sinuses, the basivenales. The tergal sclerites were derived from the tergum as follows: the lateral part of the tergum became incised into five lobes; the prealare, suralare, median lobe, postmedian lobe and posterior notal wing process. From the tips of these lobes, five slanted tergal sclerites separated along the deep paranotal sulcus: the tegula, first axillary, second axillary, median sclerite, and third axillary. Primitively, all pteralia were arranged in two parallel series on both sides of the hinge. In Paleoptera, the series stayed more or less straight; in Neoptera, the series became V-shaped. Pteralia in Paleoptera and Neoptera have been homologized on the basis of the fossil record.A differential diagnosis between Paleoptera and Neoptera is given. Fossil evidence indicates that the major steps in evolution, which led to the origin first of Pterygota, then of Neoptera and Endopterygota, were triggered by the origin and the diversification of flight apparatus. It is believed here that all above mentioned major events in pterygote evolution occurred first in the immature stages.

Notes: Studies of the response of adult mammalian and amphibian ventricle to injury have indicated the formation of a connective tissue scar in the place of the wounded or amputated muscle. It has been demonstrated that amphibian myocytes adjacent to a wound surface, unlike mammalian myocytes, have a proliferative capacity. In the present study, a minced cardiac muscle graft was placed into the adult newt ventricle in order to increase the number of myocytes near a wound surface. With such an increased number of reactive myocytes, it was thought a new wall consisting primarily of muscle might be formed. One-sixteenth to one-eighth of the ventricular apex was removed, minced and returned to the amputation surface of the ventricle. General histological and autoradiographic studies were conducted on two sham-operated animals and on five experimental animals which were killed at 5, 10, 20, 30, 50 and 70 days after surgery. Major events of the repair and reorganization of minced cardiac muscle included blood clot formation followed by necrosis of the blood clot and much of the muscle graft. By ten days, an apparent coalescence of muscle fragments and continuity of ventricular and graft lumina were observed, although the graft area never formed an integrated unit with the wounded ventricular wall. The peak of mitotic activity (3.19%) and thymidine labeling (28.1%) of graft cells, including many cells which resembled cardiac myocytes, was observed at 20 days. At 30 days, the graft was observed as a continuous wall composed primarily of muscle fibers. Several 30-, 50- and 70-day grafts had rhythmic contractions. These results suggest that amphibian cardiac muscle has histogenetic and proliferative capacities not attributable to mammalian cardiac muscle.

Notes: An ultrastructural comparison of mouse oocytes isolated at various stages of growth and meiotic competence has been carried out. Progressive changes in the nucleoli, ribosomes, mitochondria, endoplasmic reticulum, Golgi complex, and other organelles and inclusions of the oocyte have been examined as a function of oocyte size by transmission electron microscopy. The observations presented support the idea that growth of the mammalian oocyte involves not just tremendous enlargement of the cell, but extensive alterations in its overall metabolism as reflected in the ultrastructure of the oocyte at various stages of growth.

Notes: The mammalian ovary has been studied by optical microscopy and by scanning and transmission electron microscopy with the purpose of presenting an integrated view of the differentiating mammalian follicle. During follicular development, changes in the granulosa cells are particularly noteworthy and include dramatic modifications in cell shape coincident with antrum formation. The cytoplasmic processes of those granulosa cells immediately surrounding the oocyte, as well as the more peripheral granulosa cells comprising a second and third layer, traverse the zona pellucida, infrequently interdigitate with the microvilli of the egg, and make both desmosomal and gap junction contacts with the oocyte. The zona pellucida is thus distinguished by numerous fenestrations of varying diameters. The membrana limitans (basal lamina) is a bipartite structure composed of (a) a homogeneous stratum upon which the peripheral layer of granulosa cells rests, and (b) an outer region of collagen-like fibers. The specific advantages and limitations of the different methodologies utilized to study folliculo-genesis are discussed.

Notes: The gross external morphology of the salivary glands of Gromphadorhina portentosa is described from light, scanning, and transmission electron microscopic observations. Various techniques, such as cryofracturing and epoxy-fracturing followed by plastic removal, were employed. Internally, the transportation system is characterized by a cuticle-lined lumen bordered by duct cells. The duct collects secretory products, some of which are reabsorbed by duct cells. Products are transported to intercalary ducts and eventually to the hypopharynx and/or salivary reservoirs. Transmission electron micrographs demonstrate distinctive morphological differences between duct cells bordering ductules and those which line expanded regions of the duct. Duct cells which surround ductules have a microvillous-lined apical border in which the cuticular coat of the lumen may be only partially developed. Duct cells in other regions may retain microvilli, or the apical plasma membrane may invaginate and vesiculate. In some cells the apical region has neither microvilli nor invaginations, but possesses two morphologically different forms of microtubules. Some duct cells are characterized by the presence of lamellar bodies in the nuclear region and/or collagenous material above the basal lamina in the area where the acinar duct becomes confluent with the intercalary duct. The plasma membranes between adjacent duct cells within acini become convoluted, forming loops filled with cytoplasm. These loops, along with contact and septate desmosomes formed between membranes, may serve dual functions: adherent mechanisms between cells and/or transportation of materials between cells.

Notes: Fertilization in Notophthalmus viridescens is internal and involves passage of the sperm through five layers of egg jelly (J5-J1, from outermost to innermost), each of which is secreted by a discrete region of the oviduct. Polyspermy is normal. Passage of the sperm through the jelly and into the egg was studied by a technique of artificial insemination similar to natural insemination, in that undiluted fluid from the vas deferens was applied directly to eggs with various layers of jelly present, followed by flooding with water three to five minutes later. In general, successful fertilization increased as the number of jelly layers increased; jellyless coelomic eggs were not fertilizable. Sperm passage through the jelly and into the egg usually occurs within one to three minutes. Upon hydration of the jelly, barriers to sperm penetration develop in layers J5 and J3. Changes in the egg jelly thus seem to be involved in the restriction of polyspermy to a low level.

Notes: The sperm of the shiner surfperch are packaged into high density aggregations which are introduced into the female genital tract at insemination. Germ cell differentiation occurs within cysts formed by nongerminal Sertoli cells. In late spermiogenesis, spermatozoa within the cysts come to lie parallel to each other and become more densely packed. These sperm packets (spermatophores), containing approximately 600 spermatozoa, then are released into the efferent sperm ducts.The exact nature of the spermatophore binding material is not known, but a major component is proteinaceous and is synthesized in the rough endoplasmic reticulum of the efferent sperm duct epithelial cells. The mechanism by which the spermatophores pass from cysts into ducts is not clear. It appears that whereas many Sertoli cells degenerate causing the cyst wall to break down, many Sertoli cells do not degenerate, but rather assume the configuration of columnar duct cells. The spermatophores remain intact within the testicular ducts, but rapidly dissolve within the female ducts in response to increased pH.

Notes: The telemetered electromyographic activity (EMG) of select hindlimb muscles of unrestrained cats during standing, walking, trotting, and galloping have been recorded. Simultaneous cinematographic records permitted close correlation of muscle activity and locomotor behavior. In general, the pattern of extensor activity of the ankle, knee, and hip during locomotion is fairly consistent, while that of the flexors is more variable.Changes in basic EMG patterns from walk, to trot, to gallop are most evident in the two-jointed muscles associated with the knee and hip. Progressively greater variation of activity onset and cessation can be seen among extensor muscle groups from the walk, to trot, to gallop. Co-activation of the joint extensors and flexors, especially of the hip, at the end of the stance phase (E3) is slight in the walk, moderate in the trot, and considerable in the gallop. These EMG changes are necessary to meet the demands imposed upon the musculature at the faster gaits, particularly galloping, which include limb rigidity as related to loading, momentum as related to the limb's directional change from the stance phase to the swing phase, and lower spinal movements.The peroneal muscles of the ankle and the gluteal muscles of the hip show extensor activity and act as joint stabilizers during locomotion. Both biceps femoris anterior muscle and biceps femoris posterior muscle show consistent hip extensor patterns at all gaits. During quiet standing, extensor activity about the knee, ankle, and metatarsophalangeal joints is evident; but the hip extensor and flexor musculature is remarkably silent.EMG data for unrestrained cats are compared to those of dogs on a treadmill (Tokuriki, '73a,b, '74; Wentink, '76) and those recorded from decerebrate cats (mesencephalic preparation) during controlled locomotion (Gambaryan et al., '71). The EMG patterns from decerebrate cats are more consistent at the walk and gallop within functional groups of muscles at the ankle, knee, and hip than the EMG patterns observed in unrestrained cats or animals moving on a treadmill.

Notes: The relationship of the cells and tissues which comprise the developing ovarian follicle in Xenopus laevis has been studied with scanning and transmission electron microscopy. The saclike ovary is covered on its coelomic side by a squamous epithelium. The cells of this epithelium are extensively interdigitated, and each bears a short, centrally positioned cilium. The lumenal surface of the ovary is covered with a layer of nonciliated squamous cells. The areas of cell-cell contact are characterized by desmosomes in both epithelia, and between the epithelia lies a connective tissue layer-the theca-which contains collagen fibers, blood vessels, nerves, smooth muscle cells and oogonia. Beneath the theca in each follicle lies a single layer of flat stellate follicle cells. Associations between adjacent follicle cells are intermittent, leaving wide spaces or channels. Junctional contacts between neighboring follicle cells are characterized by desmosomes. From the basal surface of each follicle cell extend long, broad macrovilli which penetrate the underlying acellular vitelline envelope and contact the surface of the oocyte. Evidence is presented which suggests that follicle cells may produce and release components which participate in the formation of the vitelline envelope which consists of a 3-dimensional lattice of ropey fibers. Passageways through the vitelline envelope allow the maintenance of contact between oocyte and follicle cells and also allow ready penetration of materials both to the oocyte (e.g., vitellogenin) and from it (e.g., cortical granule material) at different stages of its development.

Notes: This study reveals age related changes in the microscopic structure of the paired frontal bone of the domestic rabbit. Undecalcified ground sections were prepared from anterior frontal bone slices removed from New Zealand White rabbits ranging from birth to 24 months of age. Included were 40 females, 4 males and 6 rabbits less than 14 days old of unknown sex. The ground sections revealed both qualitative and quantitative age changes. Qualitative changes include change in bone tissue types and developmental processes, and presence or absence of primary and secondary osteones. Quantitative changes were measured by counting primary osteones in the outer table of each frontal bone half within 1.6 mm of the metopic suture. In this region, primary osteones were absent at birth, limited in number at 14 days and generally numerous between one and three months of age. In animals older than three months, numbers of primary osteones generally decreased with increasing age. No animals older than 16 months revealed primary osteones. Possible sources of variability in the relationship between observed primary osteone number and age include ability to recognize primary osteones, methods of sampling and processing bone slices, sex related differences and diseases afflicting specimen. Significance of this study includes increased knowledge of frontal bone growth and histology.

Notes: Light microscopic autoradiography with 3H-thymidine demonstrates that the three regions of the alimentary tract in the larval (ammocoete) lamprey, Petromyzon marinus L., possess different patterns for renewing their epithelium. In the oesophagus, columnar and mucous cells originate from stem cells located at the bases of folds and migrate to the tops of the folds where they are apparently extruded. Ciliated cells, located only at the tops of the folds, seem to differentiate from migrating columnar cells. In the anterior intestine, stem cells are present throughout the epithelium so that there is limited migration of cells and their extrusion occurs randomly. In the posterior intestine, the stem cells located at the bases of the typhlosole provide a continuous population that differentiates and migrates to the top of the typhlosole and to the opposite epithelial wall where they are presumably extruded. The rates of cell renewal in all three epithelial regions of the alimentary tract are slower in animals maintained at 10 ± 1°C compared with those kept at 21 ± 1°C. Comparatively, ammocoetes have the least specialized system for cell renewal known in the alimentary tract of a vertebrate.

Notes: The renal sac of the ascidian family Molgulidae (Tunicata, phylum Chordata) has been thought to function as a kidney, yet its structure, contents and activities seem incompatible with current generalizations regarding excretory processes in marine animals. The development of the renal sac is described here as part of a general effort to reexamine the organ's role in Molgula manhattensis. Light microscopy of living animals and fixed material has shown the following: (1) The renal sac begins to sequester concretions before the heart starts beating and before feeding begins. Therefore, blood circulation by heartbeat is not necessary for production or transport of the initial concretions, whatever its effects may be on the renal sac in older individuals. Ingested food cannot provide the initial concretion material. (2) In laboratory-raised animals, concretions appear in the renal sac before “renal sac organisms” (fungus-like organisms seen in the renal sac of all field-collected adults) can be detected. Thus, at least some portion of the concretions can be produced by Molgula in the absence of renal sac organisms. (3) No openings have been detected in the renal sac at any stage of its development, nor is there any evidence that concretions are dissolved or transported out of the renal sac. (4) The development and morphology of the renal sac are consistent with the hypothesis that the organ is an epicardial derivative, except that the renal sac arises from post-pharyngeal (presumptive gut) endoderm, rather than pharyngeal endoderm.

Notes: Oocytes and nurse tissue of Bruchidius differentiate from germ cells during the extended period of pupal development (7.2 ± 0.6 days). A system of 15 pupal stages correlates ovarian development with changes in pigmentation of the eyes, maxillae, alae and tarsalia. The ovarioles grow in length at a constant rate, though their width does not change.A differentiating zone, consisting of germ cells and the basal layer of interstitial cells, arises at the base of the tropharium and separates presumptive oocytes and nurse cells. Early in pupal development the germ cells are arranged in primary syncytia with the cells connected by persisting intercellular bridges filled with fusomal material, never with larger particles, such as mitochondria. At later stages membrane disintegration changes the primary syncytium into a secondary one including all nurse cell nuclei.Nutritive cords are first noticeable when differentiation of oocytes and nurse cells starts. The cords seem to be of primary origin, i.e., they are connections between sister cells which become elongated as these cells are separated during growth. This is indicated by the persistence of intercellular bridges which are sometimes found as part of the membrane of growing nutritive cords connecting young oocytes with the nurse cell syncytium.

Notes: The formation of protein-carbohydrate yolk in the statoblast of a fresh-water bryozoan, Pectinatella gelatinosa, was studied by electron microscopy. Two types (I and II) of yolk cells were distinguished. The type I yolk cells are mononucleate and comprise a large majority of the yolk cells. The type II yolk cells are small in number; they become multinucleate by fusion of cells at an early stage of vitellogenesis. In both types of yolk cells, electron-dense granules (dense bodies) are formed in Golgi or condensing vacuoles, which are then called yolk granules. For the formation of yolk granules, the following processes are considered: 1. Yolk protein is synthesized in the rough-surfaced endoplasmic reticulum (RER) of the yolk cells. 2. The synthesized protein condenses in the cisternal space of the RER and is packaged into small oval swellings, which are then released from the RER as small vesicles (Golgi vesicles, 300-600 A in diameter). 3. The small vesicles fuse with one another to form condensing vacuoles, or with pre-existing growing yolk granules. 4. In the matrix of the condensing vacuoles or growing yolk granules, electron-dense fibers are fabricated and then arranged in a paracrystalline pattern to form the dense body. 5. After the dense body reaches its full size, excess membrane is removed and eventually the yolk granules come to mature. Toward the end of vitellogenesis of the yolk cells, the cytoplasmic organelles are ingested by autophagosomes derived from multivesicular bodies and disappear.

Notes: Testis structure in four species of goodeid teleosts is described. Testicular tubules terminate blindly at the testis periphery where spermatogonia are located. In goodeid teleosts, development of sperm takes place synchronously within cysts whose periphery is made up of a single layer of Sertoli cells. Upon completion of spermiogenesis, spermiation ensues wherein sperm are shed, as spermatozeugmata, into the testis efferent duct system. Subsequently, Sertoli cells, which comprised the cyst periphery, transform into efferent duct cells.Sertoli cells phagocytize residual bodies and are involved in the formation of spermatozeugmata. The structure of the goodeid spermatozeugmatum is quite different from that observed in the related poeciliids. It is concluded, in view of this and other considerations, that the goodeids and poeciliids have independently evolved solutions to the problems of internal fertilization and gestation.

Notes: The papillae basilares of 12 species of lizards from seven different families were studied by SEM. The iguanids, Sceloporus magister and S. occidentalis, have typical “iguanid type” papillae with central short-ciliated unidirectional hair cell segments and apical and basal long-ciliated bidirectional hair cell segments. These species of Sceloporus are unique among iguanids in that the bidirectional segments consist of but two rows of hair cells. The agamids, Agama agama and Calotes nigrolabius, have an “agamid-anguid type” papilla consisting of an apical short-ciliated unidirectional hair cell segment and a longer basal bidirectional segment. Agama agama is unusual in having a few long-ciliated hair cells at the apical end of the apical short-ciliated segment. The agamid, Uromastix sp., has an “iguanid type” papilla with a central short-ciliated unidirectional segment and apical and basal bidirectional segments. The anguid, Ophisaurus ventralis, has an “iguanid” papillar pattern with the short-ciliated segment centrally located. All the short-ciliated hair cells of the above species are covered by a limbus-attached tectorial network or cap and the long-ciliated hair cells, only by loose tectorial strands.The lacertids, Lacerta viridis and L. galloti, have papillae divided into two separate segments. The shorter apical segment consists of opposingly oriented, widely separated short-ciliated cells covered by a heavy tectorial membrane. The apical portion of the longer basal segment consists of unidirectionally oriented hair cells, while the greater part of the segment has opposingly oriented hair cells.The xantusiids, Xantusia vigilis and X. henshawi, have papillae made up of separate small apical segments and elongated basal segments. The apical hair cells are largely, but not exclusively, unidirectional and are covered by a heavy tectorial cap. The basal strip is bidirectional and the hair cells are covered by sallets. The kinocilial heads are arrowhead-shaped.The papilla of the cordylid, Cordylus jonesii, is very similar to that of Xantusia except that the apical segment is not completely separated from the basal strip.The papilla of the Varanus bengalensis is divided into a shorter apical and a longer basal segment. The hair cells of the entire apical and the basal three quarters of the basal segment are opposingly oriented, not with reference to the midpapillary axis but randomly to either the neural or abneural direction. The apical quarter of the basal segment contains unidirectional, abneurally oriented hair cells. The entire papilla is covered by a dense tectorial membrane.The functional correlations of the above structural variables are discussed.

Notes: The circulatory systems of four polystyelids, Botryllus schlosseri, B. primigenus, Botrylloides violaceus and Symplegma reptans, were compared. The palleal buds are connected to the parent zooid by a peduncle and to the colonial vascular system by connecting vessels. The peduncle of S. reptans disappears at an earlier stage of bud development than in B. primigenus; it survives the dissolution of the parent zooid in B. schlosseri and B. violaceus. The connecting vessel is formed by anastomosis between an epidermal outgrowth from the bud and a neighboring colonial vessel, and is characterized by the presence of a sphincter. The number of connecting vessels formed in a palleal bud is three in S. reptans, two in B. primigenus and one each in B. schlosseri and B. violaceus. In each species, the larva has eight rudiments of ampullae. In B. primigenus, the original ampullae degenerate soon after metamorphosis and new ampullae extend from the ventral epidermis of the oozooid. In the other species, the colonial vascular system is derived from the original ampullae.The whole colonial vascular system contracts and expands periodically, with regionally different phases. During each expansion cycle, the sphincter contracts once in B. primigenus and twice in S. reptans. The correlation may be due to blood pressure and the propagation of excitation through the colonial vascular system.

Notes: Scale neogenesis following excision of pieces of skin of various sizes and shapes has been studied in several squamate species. In small wounds, neogenesis does not occur, the wound region contracts, and increased areas of hinge differentiation are seen. In large wounds, the time taken for neogenesis to occur, and the size, shape, distribution, and number of the reformed units, are variable. We confirm previous reports that neogenesis accompanies a renewal phase of the shedding cycle, and suggests that this is because both types of morphogenesis require germinal stability.All types of trauma thus far studied show the initial formation of a hyperplastic wound epithelium with the histological characteristics of a normal α-layer: such tissues are the basis for physiological barrier functions. The mechanical functions of the skin can be fairly adequately restored even by abnormal neogenic scales. The observed variability in the process of scale neogenesis, and the final form of the individual units, are argued to be the result of mechanical factors impinging on the differentiating tissues.

Notes: The stages in wound healing of the wax-moth, Galleria mellonella, were examined using routine histological techniques. Final instar larvae were wounded and maintained for up to 72 hours before fixation, dehydration and embedding in Paraplast wax or Araldite.Immediately after wounding both fat-body and hemolymph were forced through the wound to form a plug. Concomitantly, the hemolymph coagulated forming vast networks of strand-like material attached to the hemocytes underlying the wound. After one to two hours this plug melanized and the cells became highly necrotic. Six hours after wounding, there was a massive influx of hemocytes which eventually attached to the melanized layer over the wound to form a multicellular sheath. Twelve to twenty-four hours later, the epidermal cells underlying the broken cuticle detached and migrated across the wound to form a new intact layer. This layer secreted an amorphous material which is probably the precursor of the new cuticle. Hemocyte functions during wound healing and other cellular defenses are discussed.

Notes: Time-lapse cinemicrography was used to show what changes in the number, size, shape, arrangement and what movements of apices of superficial cells occur during epiboly, extension, convergence and blastopore formation in the blastula or gastrula of Xenopus laevis. Epiboly of the animal region occurs by apical expansion of superficial cells at a nearly constant rate from the midblastula to the midgastrula stage. Egression of deep cells into the superficial layer does not occur. Extension of the dorsal marginal zone begins in the late blastula stage with the rapid spreading of the apices of cells in this region and this continues until the onset of neurulation when rapid shrinkage begins. Extension and convergence of the dorsal marginal zone occurs by a rearrangement in which individual cells exchange neighbors and by a change in the shape of the cell apices. Regional differences in apical expansion are accompanied by differences in rate of anticlinal division of superficial cells such that cells in all sectors of the animal region and the marginal zone show similar patterns of decrease in apparent apical area. Shrinkage of the apices of bottle cells during blastopore formation is described. From this and other studies, a model of the cellular behavior of epiboly, extension and convergence is constructed and several hypotheses as to how these activities might generate the mechanical forces of the gastrulation movements are presented.

Notes: The digestive tract of Hoplosternum thoracatum consists of an esophagus, gastric area, anterior digestive intestine with elaborate folds, digestive intestine with decreasing folds and thin, smooth-surfaced respiratory intestine. The upper tract has a mucoid columnar lining which is gently folded, whereas the gastric area has numerous pits opening into the tubular secretory glands. Striated muscle comprises the anterior muscularis but is replaced by inner circular and outer longitudinal smooth muscle layers in the gastric region. The digestive intestinal mucosa is elaborately folded, consisting of columnar cells with prominent brush borders. Mucosa, submucosa, circular and longitudinal muscularis and serosa layers are present throughout the tract. Goblet cells occur in both the digestive and respiratory intestine. Major changes that appear in the respiratory intestine are a drastic reduction in mucosa epithelial thickness and the penetration of an elaborate capillary bed into the epithelium. The other basic layers are not significantly reduced in thickness. The air-blood barrier consists of the thin epithelium, basement lamina and very thin capillary endothelium. Regional cellular composition and ultrastructural features are correlated with respective digestive and respiratory functions.

Notes: The morphology and microscopic anatomy of the reproductive organs and colliculus seminalis of the male rabbit are described and illustrated. Special attention is given to the accessory sex glands, because not all have been accurately identified previously. The terminology suggested for the accessory glands (with other terms commonly used in the literature in parentheses) follows: glandula vesicularis (glandula seminalis, vesicula seminalis), proprostata (glandula vesicularis, coagulating gland, prostata), prostata, paraprostata (glandula Cowperi superior), glandula bulbourethralis (glandula Cowperi inferior). The English equivalents are vesicular, proprostate, prostate, paraprostate and bulbourethral glands. Organs were obtained from 39 adult Dutch-belted rabbits that averaged 2,023 g in bodyweight. Organ weights (means and standard deviations) were as follows: testis, 2.035 ± 0.529 g; caput epididymidis, 0.264 ± 0.087 g; corpus epididymidis, 0.046 ± 0.019 g; cauda epididymidis, 0.398 ± 0.123 g; proximal part of the ductus deferens, 0.098 ± 0.026 g; ampulla of the ductus deferens, 0.177 ± 0.069 g; vesicular gland, 0.529 ± 1.169 g; proprostate gland, 0.633 ± 0.304 g; prostate gland, 0.411 ± 0.181 g; paraprostate gland, 0.040 ± 0.019 g; bulbourethral gland, 0.390 ± 0.133 g; and epididymal fat pad, 0.545 ± 0.339 g. Correlations among organ weights were calculated and interrelationships among them and bodyweight are discussed.

Notes: Early embryonic mitosis of the silkworm, Bombyx mori, was morphologically studied in the normal eggs and in the eggs treated by low temperature (-10°C).The first embryonic mitosis is observed in the eggs at 120 to 150 minutes after deposition at 26°C. After egg and sperm pronuclei unite, a spindle is formed in each of the pronuclei independently. At metaphase and anaphase paternal and maternal chromosomes are in separate groups on a spindle (gonomeric) and karyogamy takes place at telophase when they reach the poles.The second embryonic mitosis is shown in the eggs at 180 to 210 minutes after deposition. The division of two nuclei is not synchronous in the silkworm, and the mitosis is not gonomeric.In the eggs treated by low temperature, spindle fibers are not observed at all at -10°C, and chromosomes, which form two deeply stained masses of irregular shape, are seen in the less stained area of spindle shape. When the eggs are returned to 26°C, some eggs go into normal gonomeric division, while some form two small and compact spindles, which seem to be derived from each of the pronuclei. It was observed that these compact spindles are able to continue mitosis.

Notes: The simultaneous demonstration of lysozyme using the unlabelled antibody enzyme method and mucosubstances by staining with the periodic acid-Schiff (PAS) and Alcian Blue pH 2.5 techniques has led to the identification of a new subpopulation of mucus-producing cells containing lysozyme in small intestinal specimens from normal rats and from patients with inflammatory bowel diseases. These cells, containing both mucosubstances and lysozyme, are located in the lateral walls of the crypts of Lieberkuhn, but can occasionally be found also in or near the tips of the villi. The specific staining for lysozyme was observed in the apical and/or basal cytoplasm of these mucus-producing cells and was readily detected in sections counterstained for mucosub-stances with Alcian Blue. The localization of these mucus-producing cells was similar both in the normal rat and in the pathological human specimens. Absorption controls and controls where a non-immune serum was substituted for the specific antilysozyme serum confirmed the specificity of the lysozyme localization.

Notes: Development of porcine conceptuses included transitions of five stages: blastocysts of spherical, ovoid, and tubular forms containing an embryonic disc and trophoblast, extremely elongated filamentous blastocysts, and stages of embryogenesis between days 9 and 18 after mating. Embryonic survival was reduced by 17% during this period. In this litter-bearing species, intense alteration in distribution patterns occurred at days 11 and 12, when blastocysts rapidly elongated to filamentous forms. Increased embryo mortality did not result from rapid changes in distribution patterns of conceptuses within the same uterine horn at this time. Filamentous blastocysts quickly reached lengths often exceeding 60 cm, and these conceptuses became regularly spaced with no overlap of tubular membranes from other embryos in that horn. The number of concep-tuses within a uterine horn ranged from 1 to 13. Protein in individual concep-tuses was used as an indicator of growth and denoted exponential increase, but at a lower rate for blastocysts of spherical, ovoid, and tubular forms as compared with that found in filamentous blastocysts and embryogenesis stage conceptuses. Growth of a conceptus, based upon its protein content, was independent of the developmental stage or potential loss of those neighbors nearest that conceptus.

Notes: The development of the middle ear and tympanum of Gallus gallus has been studied in embryos Hamilton-Hamburger stages 20-46. Particular attention was paid to the pattern of expansion of the pharyngeal pouch forming the tympanic cavity, and the histogenesis of the tissues of the region of the vestibular window. It is concluded that pouch expansion is brought about by simple epithelial growth into regions devoid of mesenchyme. The mesenchyme does not show significant cell death, but differentiates as connective tissue, macro-phages, and sinus vascular spaces. The epithelium of the mature cavity is of endo-dermal origin, and there is no indication of celomic contributions. We provide a detailed morphological analysis of the development of the footplate from cells of both the second visceral arch and the otic capsule. These detailed observations on the patterns of chondrification of columella and capsular tissues permit the presentation of a model for cellular interactions leading to the differentiation of the annular ligament.

Notes: The prefusion epithelium of human palatal processes was examined for evidence of specialization which might facilitate epithelial adherence with the opposing palatal process. A surface coat stained with ruthenium red (RR) was found on all apical aspects of the palatal epithelium. In the prefusion regions, RR staining was also observed in the spaces between the superficial cells of the epithelium and in necrotic cells. Adjacent oral and nasal epithelium excluded the RR below the level of the apical junctional complex. In the absence of RR, a dense material was observed in the most superficial intercellular spaces of the prefusion region. Many superficial cells in the area were in various stages of necrosis. The combination of degenerating surface cells and an accumulation of a poly-anionic substance such as glycoprotein may facilitate epithelial adherence between opposing human palatal processes.

Notes: Normal, rachitic, and vitamin D3-replete chicken growth plates were studied utilizing the potassium pyroantimonate-osmium tetroxide procedure. A marked membrane and mitochondrial calcium was revealed in all specimens in the maturing and early hypertrophic zones which disappeared as heavy matrix mineralization began.The most significant difference shown in the specimens was in the marked intracellular lipid content of chondrocytes in all zones of the rachitic and D3-replete growth plates. There was negligible lipid present in normal specimens.It is suggested that as most of the mechanisms postulated as necessary for calcification are present in rachitic chicks, perhaps the increased intracellular lipid pool results from the formation of abnormal lipids for insertion into the plasma membrane and thus prevents normal calcium transport.Chains of intracellular vesicles were also visualized in maturing and hypertrophic chondrocytes. These were more often seen in rachitic growth plates and in increased numbers in the early D3-replete specimens. The etiology is unknown at the present time.

Notes: At least six different types of nuage, as judged by morphological appearance, were found in spermatocytes of the adult rat testis. These were characterized by form, distribution, and association with other organelles. The appearance (with time) and the dissociation of some nuage types were recorded in conjunction with other events of the spermatogenic cycle. The data indicate that all types of nuage behave in a dynamic way. Especially interesting were the findings concerning the chromatoid body. This structure was first observed in mid-pachytene spermatocytes. By late diplotene and during the first meiotic division, it had lost its prominence such that its eventual fate could not be determined. Large dense (0.5 μm) bodies appeared de novo in the cytoplasm of newly formed secondary spermatocytes. They were seen scattered throughout the cell and in association with mitochondria. With time these bodies appeared to coalesce to form the large definitive chromatoid of a type similar to that known to be present throughout most of the remainder of spermiogenesis.

Notes: Dorsal roots and spinal ganglion cells of adult cats were studied for acetylcholinesterase (AChE) content. An inverse correlation exists between cell size and AChE activity; large neurons are AChE-negative whereas small ones are intensely AChE-positive. A few AChE-positive fibers were demonstrated in the dorsal roots. A possible correlation between AChE activity and substance P content of primary sensory neurons is discussed.

Notes: The actions of the deep and superficial portions of the ptery-goideus muscle and the depressor mandibulae were studied in the agamid lizard, Uromastix aegyptius, using fine wire electrodes. The EMG signals were recorded, while simultaneously recording the jaw positions during feeding on movie film at 32 fps. Muscle activity varies with different types of food. The deep and superficial portions of the pterygoideus performed different functions. The deep ptery-goideus functioned during opening of the jaws, presumably to protract the jaw. The superficial pterygoideus was strictly a jaw elevator. The depressor mandibu-lae is not the initiator of jaw opening. When biting on tough food items, the deep pterygoideus and depressor mandibular were active.

Notes: The L-proline analog, L-azetidine-2-carboxylic acid, (LACA) was injected into embryonated eggs of the common fowl, Gallus domesticus at daily doses of 350 μg/egg on one or several days between 8 and 12 days of incubation. Treatment at nine-days of incubation preferentially retarded embryonic growth to the twelfth day but recovery of growth rate occurred by 15 days of incubation. Relationships between growth and LACA-inhibited aspects of collagenogenesis are discussed.The earliest aged embryos from which isolated stem cells from membrane bones will form secondary cartilage is ten days of incubation. Secondary chondro-genesis on the quadratojugal, a membrane bone of the skull, was inhibited by treatment of whole embryos with LACA at nine days of incubation but not by treatment at eight days. We concluded that an event involving collagen began at nine days of incubation, was blocked by LACA, and was part of the process of chondrogenic determination of these stem cells. Addition of LACA to the medium in which already determined stem cells from the quadratojugal were cultured prevented expression of the chondrogenic phenotype. This proline analog is then a useful probe for events relating both to determination and to expression of the differentiated state, and allows conclusions to be drawn regarding the role of col-lagenogenesis in these events.

Notes: Mouse uterine glandular epithelium during the lactationally delayed implantation period and after estradiol induction of implantation was investigated using light and electron microscopy. During the delayed implantation period the lumen of this simple tubular gland is narrowed. The glandular epithelial cells have a well developed Golgi complex lateral to the nucleus, and numerous cisternae of smooth and rough endoplasmic reticula (RER) and many electron lucent apical vesicles of sizes up to 0.2 μm in diameter near the luminal border. The basal region contains lipid droplets and dispersed, irregular cisternae of RER. Twenty-four hours after the administration of 17β-estradiol the glandular lumina become dilated but the luminal content does not stain with azure B. Ultrastructurally the glandular cells are not remarkably different from those seen during the delay period. However, by 48 hours after estradiol administration the glandular lumina are not only dilated but filled with material which stains intensely with azure B and is ultrastructurally dense and homogeneous. The apical region of the glandular cells contains granules up to 0.4 μm in diameter composed of electron dense material similar in density to that seen in the glandular lumen. In addition, the Golgi complex has assumed a position apical to the nucleus, and the basal RER has an increased number and more orderly arrangement of cisternae.The changes seen in the uterine glands after the induction of implantation during the delay period are apparently indicative of increased secretory activity of the glandular epithelia. However, the contribution of the glands to the changes in uterine fluid composition has yet to be established.

Notes: The ultrastructure of myogenesis in the mouse hind limb has been studied from day 12 to birth. Mononucleated cells with myofilaments are small and infrequent during myogenesis and never line myotubes. Only mononucleated cells without myofilaments cover the myotubes and are involved in mass fusion. These mononucleated cells are pleomorphic and undifferentiated during early myogenesis. They have a heterochromatic nucleus and many accumulate mitochondria and lengthen during days 16-18. After day 18 they are normally elongate with a heterochromatic nucleus and packed with free ribosomes. The multinucleated cell development may be divided into four stages. 1. Immature myotube (days 14-15). Their fibrils are small, out of register and some poorly defined. Many myofilaments are not in rigid hexagonal alignment. The sarcoplasmic reticlum is simple and randomly oriented and triads are absent. Large clumps of glycogen occur between euchromatic nuclei which are in chain formation. 2. Mature myotube (days 16-18). Small groups of fibrils show alignment. Glycogen granules and sarcoplasmic reticulum become numerous between fibrils. Triads are sparse and mitochondria cluster in subsarcolemmal regions and between nuclei. 3. Young myofibers are present by day 19. More fibrils are aligned and compact. The filaments are in a rigid hexagonal array, the glycogen is dispersed and nuclei are peripherally located and moderately heterochromatic. Triads are frequent but often obliquely oriented and mitochondria are elongate and numerous between fibrils. 4. Mature myofibers occur postnatally (2 weeks).

Notes: Electron microscopy of the normal human thymus demonstrates a supporting framework of epithelial-reticular cells with long branching cytoplasmic processes joined by desmosomes. In the interstices of the epithelial-reticular cell processes lie lymphocytes, macrophages, and rare myoid cells. Both small and large lymphocytes are evident. No desmosomes are observed between the lymphocytes and the epithelial-reticular cells. Macrophages are most numerous in the cortex where they often contain phagocytized nuclear debris. The possible functional significance of the above-described fine structural features is discussed.

Notes: The innervation of the rat cornea was investigated electron microscopically after KMnO4 fixation. Myelinated nerve fibres were observed only in the limbal margin of the cornea, whereas the axons located in the stroma of the avascular cornea were surrounded by the Schwann cell cytoplasm. Axon profiles with small (300-500 A) granular vesicles and another type with agranular vesicles were seen among the non-vesiculated fibres in all parts of the cornea. After superior cervical ganglionectomy it was not possible to find any axons with small granular vesicles. On the other hand, some degenerating axon profiles were observed in the stromal nerve trunks after ganglionectomy. In the epithelium-naked axons with an occasional mitochondrion and a few agranular vesicles penetrated between the epithelial cells. Moreover, axons filled with several mito-chondria were rarely observed in the epithelium, but these were difficult to differentiate from the surrounding epithelial cells.The role of the different nerve types observed in the cornea is discussed. The results suggest that the rat cornea has a dual vegetative innervation.

Notes: In mature rat soleus muscle it is shown that satellite cells are not evenly distributed over the surface of myofibers but are more numerous in the vicinity of the motor endplate. In this location they commonly lie close to the post synaptic membrane where they are termed perisynaptic satellite cells. In developing muscle several satellite cells may be seen close to the endplate and give the impression of limiting the spread of the axon over the myofiber. In addition these satellite cells make close plasmalemmal contact with Schwann cells and appear as a continuation of the Schwann sheath onto the surface of the myofiber.

Notes: Prolactin is known to enhance the uptake and metabolism of testosterone in male accessory sex organs and to increase the weight of accessory sex organs from castrated rats over those from controls treated with testosterone alone. The present study was directed toward defining fine structural changes detectable with scanning and transmission electron microscopy which might accompany such responses. Accordingly, rat ventral prostrate gland was examined from castrated animals which had received testosterone propionate and ovine prolactin singly or together, or which had received vehicle only. Unoperated ani-mals served as additional controls. Post-castration glandular atrophy was not influenced by prolactin treatment alone. Testosterone restored epithelial height, secretory product, Golgi complexes and rough endoplasmic reticulum, such that cellular and tissue morphology was generally indistinguishable from that of unoperated controls. Prostatic tissue from animals given testosterone and prolactin simultaneously exhibited pleomorphic, cytoplasmic apical projections which extended into the acinar lumen. Transmission electron microscopy demonstrated that these blebs were devoid of organelles and microvilli; scanning electron microscopy revealed that the blebs were highly wrinkled and more numerous than were the projections observed in tissue from animals treated with testosterone alone, or in tissue from unoperated controls. It is suggested that such blebbing may reflect enhanced apocrine secretion in prolactin/testosterone stimulated restoration of the prostate gland in castrated rats.

Notes: An electron-opaque substance, lanthanum, was utilized to determine when germ cells of the rat first cross the blood-testis barrier in adult spermatogenesis. Intravascularly perfused lanthanum was shown to surround all spermatogonia, preleptotene spermatocytes and early leptotene spermatocytes of Stage IX in the adult rat testis. Lanthanum was excluded from the spaces around more mature cells by newly-formed tight junctions between adjoining Sertoli processes. These processes had previously intervened between the leptotene cells and the basal lamina. The results are in close agreement with those of a previous study (Russell, '77a) which indicated that leptotene cells are the first cells of adult spermatogenesis to enter the intermediate compartment and to reside beyond a permeability barrier.

Notes: The purpose of this study was to examine some cytological features of guinea pig amniotic epithelium which may be related to epithelial permeability. In addition to fine structural studies, the amnion was stained with ruthenium red to demonstrate the glycocyalyx and exposed to an exogenous protein (peroxidase) to ascertain some of the permeability characteristics of the intercellular junctions. The apical microvillous border had a distinct glycocalyx of filaments 3-5 nm in diameter and up to 0.3 μm in length. These filaments stained with ruthenium red as did a narrower zone of glycocalyx adjacent to the outer leaflet of the plasma membrane. Epithelial cells were joined laterally by numerous desmosomes and by tight junctions; no evidence of a classical junctional complex was observed. When cells were exposed to ruthenium red or peroxidase, the tracer was impeded in its penetration between cells, probably by tight junctions. The presence of tight junctions indicates that the intercellular space is not continuous from the amniotic cavity to the underlying connective tissue, and undoubtedly the junctions play a role in controlling transepithelial permeability. The experiments with peroxidase also demonstrated the capacity of the cells to endocytose protein, especially at their lateral and basal surfaces. Late in gestation, increasing numbers of cells underwent cytological changes similar to cells undergoing keratinization. These changes included the disappearance of most of the cell organelles and the thickening of the plasma membrane by the addition of an electron-dense layer to the inner (cytoplasmic) leaflet. The apparent keratinization of cells may result from increased abrasive trauma caused by the fetus or may be related to accumulation of various waste products in the amniotic fluid. In any event, the cytological modifications, especially of the plasma membrane, may indicate a change in cell permeability properties late in gestation.

Notes: The histogenesis of the popliteal lymph node in the rat and the popliteal and inguinal lymph nodes in the rabbit was examined by light microscopy. Special emphasis has been laid on the initial lymphocyte population in the lymph node anlage. In the rat on the seventeenth day of gestation lymphoid cells populate a limited mesenchymal area along the vein wall. The next day the mes-enchyme shows a bulb-shaped outgrowth causing an indentation in the wall of a lymph vessel, running parallel to the vein and having a saccular widening at this place. The bulb-shaped lymphoid outgrowth fills up the widened lymph vessel; the subcapsular sinus originates from the remaining parts of the lymph vessel. At birth the lymph node can be divided into a primitive cortex consisting of an area with evenly scattered lymphocytes among the basic network of reticular cells and a medulla. About three days after birth an ovoid area containing a dense concentration of lymphocytes is observed in the inner cortex. In the next days it expands in both lateral and medullary direction but not into the outer cortex. Primary follicles appear in the outer cortex 18 days after birth.The development of the inguinal and popliteal lymph nodes in the rabbit shows the same characteristics as the histogenesis of the popliteal lymph node in the rat.The morphogenesis of the lymph node is summarized in a schematic diagram.

Notes: Adrenergic and acetylcholinesterase (AChE)-positive nerves were studied in the rat ovary four days after various experimental denervation procedures. Ablation of pelvic parasympathetic nerves (pelvic neurectomy [PN]) or abdominal vagotomy (AV) had no obvious affect on the adrenergic or AChE-positive nerves in the ovary. Section of the mesovarium resulted in the loss of all histochemically demonstrable adrenergic and AChE-positive nerves. Chemical sympathectomy with 6-hydroxydopamine (6-HD) resulted in the loss of all histo-chemically demonstrable adrenergic nerves. A few AChE-positive nerves remained in the hilar and medullary regions following chemical sympathectomy. When the presumptive parasympathectomy procedures (AV and PN) were combined with chemical sympathectomy, again no adrenergic nerves remained, however a few hilar and medullary AChE-positive fibers persisted after sympathec-tomy plus PN, but no AChE-positive fibers were demonstrable in the AV plus 6-HD group.These findings show that most of the AChE in ovarian nerves is localized in adrenergic nerves. It is suggested that the few AChE-positive fibers remaining in the ovarian hilar area after 6-HD treatment or 6-HD plus PN are derived from the vagus. These few AChE-positive nerves may be postganglionic vagal parasympathetic or they may be sensory fibers.

Notes: Supraependymal cells in the third ventricle of neonatal male and female rats were examined with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Supraependymal cells in the third ventrical of adult male rats were also studied with SEM. Many neonate supraependymal cells were round to oval in shape and exhibited varying degrees of surface irregularity. Small finger-like processes or narrow pseudopodia projected from the cell bodies over the underlying ependymal cells. Some neonatal supraependymal cells exhibited flattened cell bodies with broad pseudopodia and few surface irregularities. TEM revealed a variety of cell profiles. Prominent within the cytoplasm of many supraependymal cells were lysosomes, smooth and coated vesicles suggesting pinocytosis, subplasmalemma vacuoles, and occasional lipid droplets. The morphological characteristics of neonatal supraependymal cells suggested they were mononuclear phagocytes. Adult supraependymal cells exhibited more pleomorphic cell shapes with numerous cell processes, varying widely in size and shape, and often extending over the ventricular surface for considerable distances. These observations, in combination with previous studies by other investigators, suggest that some adult supraependymal cells may also be phagocytic in nature. The differences in morphology between adult and neonatal supraependymal phagocytes may relate to the differing third ventricle environment between adult and neonates and/or differences in the origin of the phagocytes with age.

Notes: Freeze-fracture replication technique was utilized to study the morphology of type II alveolar epithelial cells and alveolar contents in the late gestation of rabbit fetuses. It was shown that the lamellar inclusion bodies of type II cells were enveloped by the usual type of unit membrane with membraneassociated particles of 15 nm diameter. The interior of the inclusion bodies was composed of multiple stacks and/or whorls of membranes which were devoid of membrane-associated particles. Small vesicles within the inclusion were found more frequently with this technique than in chemically fixed thin-sectioned preparations.The intra-alveolar contents were comprised of two components; spherical bodies, which were identical to the internal contents of the lamellar bodies of type II cells, and tubular elements. These tubules most often appeared rectangular on cross-fractured faces. Triangular and hexagonal fracture faces were also noted. The tubules were seen to rest on the surfaces of the spherical components. Our observations suggest that the tubular element of the alveolar contents is formed through the interaction between the discharged lamellar body content and the alveolar fluid, and further suggest that at least the major constituent of type II cell lamellar bodies is lipid not bound to protein.Three new observations were made in this study; the absence of membraneassociated particles on the interior of the lamellae of the inclusions, the crossfractured profiles of tubular elements of the alveolar contents, and the occasional multicompartmental nature of type II cell inclusions.

Notes: Enriched fractions of chloride cells with good ultrastructural integrity have been obtained from gill filaments of the euryhaline teleost, Lagodon rhomboides. The branchial epithelium from seawater-adapted fish was dissociated by gentle mechanical means in a Ca++, Mg++ -free balanced salt solution. Density gradient centrifugation of the mixed cell suspensions through a Ficoll gradient yielded a fraction containing between 50 and 70% chloride cells. This fraction showed a 3- to 4-fold enrichment over comparable gill homogenate values for sodium plus potassium-activated adenosinetriphosphatase, (Na+, K+-ATPase), an enzyme concentrated in chloride cells. Isolation of chloride cells from fish adapted to one-third seawater was less successful, due to the smaller size and reduced number of these cells, although fractions with at least a 2-fold enrichment of the enzyme were obtained. These results continue to support the belief that chloride cells are responsible for the osmoregulatory activity associated with the branchial epithelium of teleosts and that this vital function is mediated through the activity of the transport associated enzyme, Na+, K+ -ATPase, the specific activity of which increases with osmotic stress.

Notes: Heavy meromyosin (HMM) labeling was used to identify the nature of the filaments which form bundles in the cytoplasm of the pericytes in brain tissue. Rat brain tissue pieces were incubated in glycerol solutions at 4°, and then transferred into buffer (pH 7.0), (1) without HMM, (2) with HMM, (3) with HMM + 5 mM ATP, and (4) with HMM + 2.5 mM Na+ pyrophosphate. In pericytes from untreated tissue, smooth-surfaced microfilaments, averaging 6 nm in diameter, appear to branch and anastomose and to anchor on the plasma membrane. After exposure to HMM, the number and the density of the microfilaments are strikingly increased. These tightly-packed microfilaments are now heavily coated with exogenous HMM thus increasing in width to 18-20 mm. They intertwine in closely-woven networks. After incubation in HMM solutions containing ATP or Na+ prophosphate, they are no longer coated with thick sidearms. It can thus be concluded that these microfilaments are of actin-like nature. In addition, after incubation in ATP, they are intermingled with, and converge onto the surfaces of, thick, tapered filaments, which we have tentatively identified as of myosin-like nature. Thus, it appears that certain of the major elements necessary for contraction are present in brain pericytes.

Notes: Cilia in neonatal canine articular chondrocytes were studied using morphometric techniques and transmission electron microscopy. The cilia in chondrocytes were morphologically similar to cilia in a variety of other cell types. A chondrocytic cilium consisted of a basal body and a ciliary shaft. The cylindrical basal body was 0.21 μm (S.D. = 0.01 μm) in diameter, 0.50 μm (S.D. = 0.03 μm) in length and contained nine microtubular triplets. The ciliary shaft was 0.196 μm (S.D. = 0.02 μm) in diameter and 1.76 μm (S.D. = 0.80 μm) in length. The number of microtubular doublets in the ciliary shaft varied depending on where along the length of the shaft the section was taken.This study demonstrates that on the average the frequency of cilia in neonatal articular chondrocytes, as estimated stereologically, was about one cilium per cell.

Notes: Bone marrow from adult rats fed a vitamin B6 deficient diet for two weeks was found to have reduced numbers of neutrophils, erythroid cells and small lymphocytes. The numbers of transitional cells were not reduced. Since the small lymphocyte population in the bone marrow consists of B cells and null cells in approximately the same proportion, it was concluded that both cell types were reduced as a result of the deficiency. A complete recovery in the cellularity of the bone marrow was brought about by returning the vitamin B6 deficient animals to a normal diet for four weeks. Other effects of the two-week vitamin B6 deficient diet included a failure to gain weight, a decrease in thymus weight and a reduction in the numbers of white blood cells in the peripheral blood. All of these defects were corrected after the animals had been fed a normal diet for four weeks.

Notes: The rough endoplasmic reticulum (RER) of Xenopus laevis hepatocytes was examined by freeze-fracture and by conventional thin section electron microscopy. Much of the RER was present as stacks of cisternae at the cell periphery but, in addition, large whorls of cisternae were seen in the cytoplasm in most sections. Freeze-fracture replicas revealed fenestrae in both stacked and whorled cisternae, although the fenestrae were more numerous in the whorls. The role of these fenestrae is unknown, but such structures would facilitate access of precursors to the protein synthetic machinery in this highly metabolically active cell type. This would be particularly important in RER whorls, where the innermost cisternae would otherwise be isolated from the rest of the cytoplasm.

Notes: Guinea pig epididymal sperm, incubated for ATPases at pH 7.0 or pH 9.0, localize reaction product on both the periacrosomal segment of the plasmalemma and the outer acrosome membrane. In other species, e.g., rabbit, Ca++-ATPase is identified with the outer acrosome membrane. It may transport Ca++ into the acrosome for activation of enzymes released during the acrosome reaction. The neutral ATPase is demonstrable on the periacrosomal plasmalem-ma and possibly modifies Ca++ concentration in the fluid around the acrosome. In guinea pig sperm, Ca++-ATPase is sensitive to centrifugation or washing of sperm which indicates that the ductal fluid has unusual properties for preservation of the acrosome. Inhibition of the enzyme by these treatments suggests that conditions on the plasmalemmal surface affect the acrosome membrane. Inability to separate reaction product on the plasmalemma from that on the acrosome membrane may be due to migration of reaction product across the periacrosomal space. However, the ATPases are elicited in the guinea pig under the same conditions as in other species. The pH 9.0 enzyme requires Ca++ while the enzyme at pH 7.0 has no ion specificities. Demonstration of these enzymes indicates that mechanisms of acrosome activation, similar to those in other sperm, are relevant to the guinea pig.

Notes: The thyroid gland of the C3H mouse is composed largely of the usual follicle but it also contains a second kind of follicle. To ascertain the embryologic origin of the cell types in each of these follicles, ventral pharyngeal outpocketings and ultimobranchial outpocketings were isolated (before they fused to form the thyroid gland) from the 12-day-old fetus of the C3H mouse. The outpocketings were implanted into different kidney capsules of adult C3H mice and were allowed to grow for several months. Transplants were then excised and examined by electron microscopy.The ventral contribution formed large aggregates of follicles and was recognized as a distinct bump on the surface of the kidney. It formed only typical thyroid epithelium arranged in follicles containing colloid. On the other hand, the ultimobranchial contribution usually formed only a small number of follicles, generally of small size. It was readily located because the follicles occurred next to a white plaque of bone or cartilage at the site of implantation. The ulti-mobranchial contribution formed follicles containing four cell types: a ciliated cell, a cell with abundant agranular reticulum, a cell with many free ribosomes and fiber and occasional hemidesmosomes, and the C cell which was the most frequent cell type. No typical thyroid epithelium was observed in the ultimobran-chial transplant.These observations suggest that the C cell in the usual follicle is derived from the ultimobranchial contribution, and that the second kind of follicle is largely an ultimobranchial contribution but the typical thyroid epithelium in it is largely or entirely a ventral contribution.