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Notes: Pyroantimonate precipitate indicates that the epithelium of the proximal tubule is the only segment of the tubular nephron of the fresh water lamprey where large accumlations of cations are distributed. Unusually large amounts of reaction product are located within the lateral intercellular spaces and within vesicles closely associated with the plasma membrane at the lateral and basal surfaces. This technique suggests the continuity of these vesicles with the plasma membrane and alludes to the possibility of an endomembranous system of vesicles and the intercellular spaces as vehicles for ion transport. Lateral intercellular spaces of proximal tubules of lower vertebrates may play a different role in kidney function that their counterparts in higher vertebrates.Osmium-zinc iodide has a specificity for certain cells within the proximal, intermediate, and distal segments, but no structural differences are noted when these cells are compared to unstained cells. Smooth endoplasmic reticulum remains unstained in the distal segment but the stain has a strong affinity for elements of the Golgi apparatus, lysosomes, and the nuclear envelope of all cell types. This technique does not suggest a structural or functional similarity between cells of the distal segment and the chloride cells of the gills of teleosts.

Notes: Anatomical analysis of the forebrain and midbrain of Anelytropsis, Dibamus and feyliniids reveals structural similarities with those of skinks and snakes. Skinks and feyliniids are probably derived from a common ancestral stock. This is suggested by mutual reduction of several telencephalic nuclei, by similar trends in the development of the dorsal thalamus, and by similarities in the lamination of their optic tecta. Anelytropsis, Dibamus, feyliniids and snakes show interdigitation of the periventricular gray zones of the optic tectum and enlargement of lamina 7 of the posterior colliculus. Of these three taxa, Dibamus is most similar to burrowing snakes and many of its brain characters are intermediate between skinks and burrowing snakes. These similarities may suggest common ancestry between Dibamus and snakes rather than parallelism.

Notes: It is possible to monitor the electrical activity of the motor neurons of Drosophila by recording the electrical activity of the muscle fibers. We have found that it is possible to specify the location of the subcuticular terminations and to describe the orientation within the thorax for the individual muscle fibers, because of the large size of the fibers and because the surface anatomy of Drosophila is known in detail. A map has been made to indicate the location of the muscle fibers with respect to superficial landmarks. The importance of the stereotaxic map for physiological studies is discussed.

Notes: The functional anatomy of pulmonary ventilation in Thamnophis elegans was studied by electromyography. Flow of air into and out of the lungs follows a triphasic pattern and occurs while the glottis is held open by a dilator muscle. Non-ventilatory rest periods characterized by a closed glottis and lack of ventilatory movements occur between breaths. Exhalation is caused by contraction of a pair of dorsolateral sheets of muscle that extends from the ventral surface of the vertebral column to the medial surfaces of the ribs and a pair of ventro-lateral sheets that extends from the medial surfaces of the ribs to the mid-ventral skin. Inspiration is powered by contraction of a series of rib levators and retractors. The last phase of the ventilatory cycle is a passive expiration that may be caused by elastic recoil of the walls of the filled lungs and relaxation of muscles used during inspiration. The site of respiratory pumping is shifted craniad after large prey items have been completely ingested. The significance of this shift and its anatomical basis are considered.

Notes: As seen in transverse section, doublet elements of the axial unit of spermatozoa of Haematolocchus medioplexus, a frog lung-fluke, possess walls made up of protofibrillar subunits 50-60 Å in diameter. The partition between A and B members of a doublet element often show extra protofibrils which may partially occlude the “lumen” of the A tubule. Each A tubule possesses outer and inner lateral arms which repeat at longitudinal intervals of about 215 Å and which appear to be structurally dissimilar; the outer arm is expanded at its free end and the inner arm often connects to the B tubule of the adjacent doublet element. Regularly-spaced radial links connect the central sheath of an inner core complex to the A tubules of the peripheral doublet elements. Tests for magnesium-activated ATPase activity provide evidence that the enzyme is associated with the surfaces of doublet elements and the surface of the central sheath. Finally, study of an axial unit which developed in an abnormal manner suggests that normal differentiation of an axial unit may depend on the elaboration of a core complex and radial links.

Notes: This is the first demonstration of an apparent acrosome reaction by the use of negative staining (phosphotungstic acid) and electron microscopy. It is also the first report of such a reaction in spermatozoa of an oligochaete annelid (Lumbricus terrestris). The morphology of the negatively stained unreacted acrosomal complexes is entirely comparable to that seen in sectioned material. After reaction, a short straight filament is extruded and the compartmentalization seen in unreacted spermatozoa is no longer visible. In the flagellar axoneme there are short cross-bridges linking the two central singlet microtubules at 150-170 Å intervals. Two fibrous elements are also present, forming, with the singlets, a tetragon. All four of these structures apparently change their elastic properties after incubation in distilled water for two hours, so that instead of following the doublet microtubules in gentle coils, the central complex components fall as a unit in jagged configurations.

Notes: Serial sections of embryonic rat eyes were stained with hematoxylin and eosin, quantified (by counting pycnotic and viable nuclei), reproduced by camera lucida on wax plates, and moulded into reconstructions in order to study the normal progression of cellular death during morphogenesis. At least nine distinct necrotic loci (A through I) can be distinguished. Immediately following contact between the retina and surface ectoderm (day 11) degenerating cells were observed in (A) the ventral extent of the optic vesicle, beginning in the mid-retinal primordium and continuing ventrally in the optic stalk, (B) in the rostral optic stalk base, and (C) in the surface ectoderm encircling the early lens placode. No degeneration was observed in the dorsal half of the presumptive retina, in the entire pigment epithelium, or in the lens placode proper. During day 11.5 the lens placode thickens and forms a degenerating locus (D) in its ventral portion opposite the underlying pycnotic zone in the retina (A). During day 12 the ventral pycnotic zone (A) divides into two subunits (A1 and A2). Invagination of the lens displaces its marginal and ventral components (C and D) so that they come to occupy the lens pore area and presumptive corneal epithelium. Simultaneous invagination of the retinal rudiment juxtaposes the pigment epithelium which concurrently forms a necrotic area (E) adjacent ventrally to that in the retina (A1). Degeneration appears in the caudal optic stalk (I). The density of viable cells decreases adjacent to pycnotic areas in the retina and pigment epithelium and increases within these death centers. During day 13 the optic fissure forms within the subunits of the ventral pycnotic zone (A1 and A2). Degenerations are seen in the dorsal optic stalk (F) and in the walls of the optic fissure (G and H). Throughout these stages necrosis appears only in those portions of the eye rudiment where invagination is either retarded or completely absent.In part, these observations suggest that cell death serves (1) to retard or inhibit invagination within death centers, (2) to integrate the series of invaginations which mould the dorsal optic cup and optic fissure, (3) to assist formation of the pigment epithelium monolayer, and (4) to orient the lens vesicle within the eye cup. The spatio-temporal relationship between necrotic loci suggests that pycnotic cells in the retina may influence their production in the lens and pigment epithelium. Preliminary observations on the mouse, pig, and human substantiate those on the rat.

Notes: The ultrastructural features of cardiac muscle cells and their innervation were examined in the tarantula spider Eurypelma marxi Simon. The cells are transversely striated and have an A band length of about three microns. H zones are indistinct and M lines are absent. Thick and thin myofilament diameters are approximately 200 and 70 Å respectively. Eight to 12 thin filaments usually surround each thick one. Accumulations of thick and thin myofilaments occur perpendicular to the bulk of the myofilaments in some cells. The Z line is discontinuous and thick filaments may pass through the spaces in the Z line. Extensive systems of sarcoplasmic reticulum and transverse tubules are present; these form numerous dyadic junctions in both A and I band regions. Sarcolemmal invaginations form Z line tubules; lateral extensions of the plasma membrane portion of these invaginations form dyads. Nerve branches of the cardiac ganglion make multiple neuromuscular synapses with at least some of the cardiac muscle cells. Both large granular and small agranular vesicles are present in the presynaptic terminals. Intercalated discs similar to those present in other arthropod hearts occur between the ends of adjacent cardiac muscle cells.

Notes: A cinematographic analysis of the unrestrained walking, trotting, galloping, jumping and landing movements of 11 adult cats was undertaken to provide previously unavailable information concerning the demands imposed on the nervous system for the control of low and high speed movements and the demands imposed by such natural movements on muscle performance and proprioceptive response.With due regard for the swing (F and E1) and stance (E2 and E3) phases of the step cycle of an individual limb, single frame analysis of the film permitted measurement of instantaneous angles of the lower spine, hip, knee, ankle and metatarsophalangeal joints. Appropriate lever arm measurements were also made on 50 freshly dispatched cats and 25 cadavers such that the Law of Cosines could be used to calculate instantaneous lengths of select hind limb muscles that would apply to the natural movements of adult cats of small (1.5-2.5 Kg), intermediate (2.6-3.5 Kg) and large (3.6-4.5 Kg) size. Muscle displacements were analyzed relative to maximum and minimus in situ lengths and the lengths associated with quiet standing. Use was also made of a previous electromyographic analysis of hind limb muscles during unrestrained locomotion (Engberg and Lundberg, '69).The sequential relations between the four phases of the step cycle are maintained as forward speed increases from walking ( 〈 2 mph) to high speed galloping ( 〉 16 mph). There are significant differences in the time consumed by each phase, however, with a greater reduction in the E3 phase, little reduction in the E2 and E1 phases and virtually no reduction in the F phase. When each phase is expressed as a relative percentage of the duration of the total step cycle, the greatest reduction is again in E3 with little change in the E2 phase. In contrast F and E1 phases increase in the percent of time they occur in each cycle, with the greatest increase in the F phase. For all speeds, analysis of the phase relations between movements of various sections of the hind limb revealed a remarkable unity of knee and ankle joint movement. The hip joint is largely out of phase with the knee and ankle during E1 and E2, all three joints being in phase in F and E3. The digits are essentially out of phase with the other joints except in the stance phase of the gallop.Rates and extents of muscle displacement during natural movements are greater than might be anticipated when expressed in absolute mm's and mm/sec but not when considered in relation to maximum and minimum in situ length and the length associated with quiet standing (Ls). During stepping a progressive increase in forward speed results in: (a) a greater usage of muscles at lengths between Ls and maximum in situ length; (b) for knee and ankle extensors, pronounced increase in the lengthening contraction associated with the E2 (yield) phase of step; and, (c) for both flexor and extensor muscles, an increased active phase of lengthening or near isometric contraction immediately prior to periods of active shortening. In contrast to these changes in active muscle status, the change from walking to galloping has little effect on the extent and rate of passive muscle displacements, particularly the F phase stretch of extensors.For the soleus muscle, calculations were made of the relation between changes in overall muscle length during natural movements and the length of the average muscle fiber and the tendon of insertion. These measurements revealed that the increases in fiber length when passive and decreases in length during active shortening are less than would be anticipated from the extensive liteature on extirpated fibers. In contrast, the increase in fiber length when active is greater than would be expected from the admittedly sparse literature on this subject.The results of this study are discussed largely in relation to two points of neurophysiological interest: the physiological range of muscle stretch as it pertains to the responsiveness of muscle spindles and tendon organs; and those mechanical aspects of lengthening contractions that give insight into the neural control of stepping. For exciting both spindles and tendon organs passive muscle stretch and shortening contractions are shown to be relatively ineffective and lengthening and isometric contractions particularly effective movements. It is suggested that, just as recent literature has emphasized the co-activation of efferent alpha and gamma motoneurons as a muscle becomes active, so too is there a synchronous activation of afferents, particularly the Ia and group II endings of muscle spindles and Ib endings of tendon organs. Finally the thesis is advanced that, while it has been convenient to separate E2 from E3 in the description of the stance phase of the step cycle, extensor muscles are actually undergoing a single mechanical event: an active stretch-shorten cycle for knee and ankle extensors and an active isometric-shorten cycle for hip extensors. This hypothesis has significant implications for the neural control program that regulates the stepping sequence in that it emphasizes the extent to which appropriate changes must be preprogrammed in the mechanical properties of muscles for the smooth execution of stepping.

Notes: Cytological and cytochemical methods were used to identify and characterzie six distinct regions of the crayfish kidney: coelomosac, labyrinth I and II, and nephridial canal I, II, and III. Cells of the coelomosac possess cytoplasm which is strongly PAS-positive, but poor in RNA and protein. Their nuclei possess unusual projections which extend to the basal plasmalemma. Labyrinth I contains columnar cells rich in glycogen. Labyrinth II is characterized by a distended lumen and by shorter cells with high cytoplasmic RNA, many possessing a large intracellular vacuole. A PAS-positive brush border is unique to the two portions of the labyrinth. Cells in the nephridial canal show strong reactions for RNA and Mg++-dependent ATPase. In nephridial canal I and II, cells are flattened to cuboidal with the lumen being more distended in nephridial canal I than anywhere else in the tubule. In nephridial canal III, the cells are large and columnar, and the cytoplasmic RNA concentration is greatest apically. Nuclei in all regions of the tubule epithelium, except coelomosac, are large and react strongly for protein. Coelomosac nuclei and those in blood cells are condensed and contain little protein. The cytoplasm of blood cells displays a significant amount of RNA, and traces of polysaccharide material.These observations demonstrate the presence of highly specialized morphological and histochemical alterations along the length of the kidney tubule and indicate sequential modification of urine in the lumen. Evident morphological and cytochemical likenesses between analogous regions of the mammlian nephron and the crayfish kidney tubule suggest that basic physiological similarities may also exist.

Notes: In the tiger salamnder the distribution of optic fibers, as revealed by the Fink-Heimer method, is compared with the localization of acetylcholinesterase, as revealed by histochemical methods. AChE activity coincides with optic nerve axons in the optic fiber layer of the retina, in the optic nerve, in the optic tracts and in every optic projection. Reginons of optic fiber terminals show heavier activity than optic fibers of passage. Comparison with other vertebrates is also made.

Notes: The spleen of the adult gerbil (M. unguiculatus) is characterized by the absence of venous sinuses and ellipsoid sheaths. The follicle (white pulp) is separated from the surrounding red pulp by a distinct marginal zone. The cell types in the marginal zone are common to both the follicle and red pulp. Separating the marginal zone from the follicle is a vascular channel of capillary dimension, the marginal sinus. A number of terminal segments of the arterial vessels within the follicle were observed to form a direct connection with the marginal sinus. Ultrastructurally, discontinuities were evident within the walls of the marginal sinus that would permit passage of both cellular and plasma components from the marginal sinus to either marginal zone or the follicle.

Notes: The innervation of each of the muscles involved in mediating head movement in the desert locust Schistocerca gregaria is described in detail. The number of motor neurones to each muscle and the neutral pathway and ganglion of origin of each are deduced from both histological and electrophysiological evidence. Only two of the muscles are, on histological evidence, innervated by as few as four different neurones, while several receive more than ten, and one at least 13. Individual muscles are shown physiologically to receive, in a few cases, as many as six different motor neurones. At least six muscles are innervated by motor neurones originating in more than one ganglion. One group of four muscles consisting in total of less than 100 muscle fibres receives more than 20 different motor neurones from three different ganglia through three or four different nerve roots. In these muscles, many single muscle fibres receive innervation from at least two different ganglia. It is concluded that the segmental nature of an insect muscle can not be deduced solely from a knowledge of the ganglion of origin of the motor innervation to that muscle. The innervation patterns that exist today must reflect past evolutionary development, but changes in the peripheral distribution of motor neurones, or migration of motor neurone cell bodies from one ganglion to another, or the development of additional motor neurones, or several of these factors together, must have formed a part of that development.

Notes: 1. Forty-eight species of oribatids in 37 families representing most of the superfamilies were collected from various environments (littoral, salt marsh, litter, sod, and freshwater) and sectioned.2. The coxal gland is composed of a sacculus and a labyrinth in all stages of all oribatid species. Muscles, originating on the body wall, insert at several points on the thin-walled sacculus which opens into the labyrinth. The labyrinth has an internal, chitinous supporting skeleton. The type A labyrinth has 3-180° bends, producing four parallel regions, and occurs in all inferior oribatids. The type B labyrinth has 1-180° bend, producing two parallel regions, and occurs in all superior oribatids. The coxal gland duct and the lateral gland duct join, penetrate the body wall, and empty into the posterior end of the podocephalic canal. All oribatids have lateral accessory glands, but only inferior oribatids have rostral and medial glands. Three ductless coxendral bodies are always present.3. The labyrinth length in oribatids is correlated with body size and the environment of the species. Oribatids from sod, leaflitter, or moss show a simple correlation of labyrinth length (X) to total body length (Y) where Y = 4.64X. Freshwater species have a labyrinth length greater than that of comparably sized terrestrial species and salt water (littoral) species have a labyrinth length less than that of comparably sized terrestrial species. There is a greater reduction in labyrinth length in species restricted to salt marshes than in species not restricted to salt marshes.4. The probable function of oribatid coxal glands is osmoregulation. Hemolymph filtration would occur across the sacculus by positive hemolymph pressure and contraction of the sacculus muscles. Resorption of ions would occur in the labyrinth, which is noncollapsible due to the internal skeleton. The hypothesis is that in freshwater species the rate of filtration is high and resorption of ions would have to be very efficient, therefore they have an elongated labyrinth; but in salt water species water loss must be minimized and preservation of ions would be a disadvantage, therefore they have a shortened labyrinth. Excre ion may also be a function of the coxal glands. The lateral gland may possibly function as an endocrine gland involved with production of a molting hormone. The rostral glands in inferior oribatids may have a salivary function.5. The coxal glands of Peripatus, some millipedes, apterygote insects, decapod crustaceans, and all arachnid orders are homologous. The Tetrastigmata, Notostigmata, Cryptostigmata, and soft ticks have typical arachnid coxal glands. The coxal glands of higher Prostigmata may be modified into salivary, silk, or venom glands. The coxal glands in Mesostigmata, Astigmata, and hard ticks are lacking or highly modified.

Notes: The blood system of the flabelligerid polychaete, Flabelliderma commensalis has been explored by dissection, light and electron microscopy and absorption spectrophotometry. The main longitudinal vessels are the dorsal, ventral, perineural, sub-oesophageal, supra-oesophageal and heart. Each segment has a segmental vessel which communicates with the dorsal vessel in thoracic setigers and the gut sinus in abdominal setigers. Branches of the segmental vessels in setigers 2-9 supply the gonads. A blood sinus envelopes most of the gut. Circulation is maintained by the pumping of the heart which immediately supplies blood to the supra-oesophageal ganglion, the branchiae and the palps. These are paralleled by a system of collecting vessels. The sinus of the supra-oesophageal ganglion receives a number of different axonal endings, some of which may be neurosecretory. The retroperitoneal vessels in their most developed form are composed of an intima, longitudinal and circular muscles and a peritoneum. The heart vessel contains a cardiac body whose cells appear to contain vacuoles of blood pigment. The blood pigment exhibits the absorption characteristics of a chlorocruorin with maxima at 438, 558 and 606 nm.

Notes: Attachment of muscle of the integument was studied in two species of Balanidae, Balanus balanoides and B. improvisus with electron microscopy. Specilalized epithelial cells (tendon cells) intervene between the muscle and overlying cuticle. An extensive desmosome-like junction exists between these two tissues. The tendon cell contains huge amounts of microtubules aligned parallel to the long axis of the inserting muscle. Tension exerted by contracting muscles is conveyed to the chitinous exoskeleton via the specially organized tendon cells and the extensive myo-tendinal cell junctions.

Notes: Among ants, Cataglyphis bicolor shows the best performance in optical orientation. Its eye is of the apposition type with a fused rhabdom. Morphological studies on the general struture of the eye as well as the effect of light have been carried out with transmission and scanning electron microscopy.An ommatidium is composed of a dioptric apparatus, consisting of a cornea, corneal process and a crystalline cone, the sensory retinula, which is made up of eight retinula cells in the distal half and of an additional ninth one in the proximal half. The ommatidia are separated from each other by two primary pigment cells, which surround the crystalline cone and an average of 12 secondary pigment cells, which reach from cornea to the basement membrane.The eye of Cataglyphis bicolor possesses a light intensity dependent adaptation mechanism, which causes a radial and distal movement of the pigment granules within the retinula cells and a dilatation of cisternae of the ER along the rhabdom.Until now, no overall order in arrangement of retinula cells or direction of microvilli has been found from ommatidium to ommatidium. Such an order, however, must exist, either on the retina or the lamina level, since we have proven the ant's capacity for polarized light analysis.

Notes: The morphology of the rectal pads of two cockroaches, Blattella germanica and Blaberus giganteus is described and contrasted with that of Periplaneta americana, studied previously. The columnar absorptive cells of the three species are similar in structure. However, Blattella and Blaberus rectal pads have a second type of cell, termed the secondary cell, that is not present in Periplaneta. The secondary cells are embedded in the pad epithelium and have crypts of cavities opening into the subepithelial sinus. In addition, a multilayered sheath is present between the pad cells and the sinus. The sheath acts as a barrier, perhaps of low permeability, between the subepithelial sinus and the pads. It is interrupted only at the borders of the secondary cells. A mechanism for fluid absorption is presented and the possible role of secondary cells is discussed. It is proposed that the secondary cells reabsorb solute from the sinus and that this solute can then be recycled through the pad cells. Structures resembling neurosecretory terminals within the cavities of the secondary cells may be involved in regulation of recycling. The arrangement of the rectal pads in these insects has structural and perhaps functional similarities with other transporting systems, particularly the cryptonephric system.

Notes: Light and electron microscope studies indicate that the old ependyma just proximal to the plane of amputation in early lizard tail regenerates shows a sequence of morphological changes which suggests that it as well as the new ependyma growing into the regenerate may play an active role in the initiation and maintenance of early tail regeneration.The old ependyma close to the plane of amputation undergoes hypertrophy and/or hyperplasia causing a partial closure of the central canal and pseudostratification. Its nuclei shift from an original apical position to a basal one. The ependymal processes become more prominent and extend to the pia, a condition not found more rostrally. There is also a significant increase in the amount of Golgi substance and a moderate increase in the rough endoplasmic reticulum. These observations lead to the thought that these cellular changes may be an expression of enhanced secretion and other activities in the old and new ependyma just proximal or distal to the plane of amputation.

Notes: Statistical analyses of chromatophore densities and morphological states in wild type, burnsi, and kandiyohi: adult Rana pipiens integument yielded the conclusion that disruptive pigmentary pattern is permanently defined by regional chromatophore densities. Spatial chromatophore patterning is enhanced and rendered more visible by the morphological and physiological differences among chromatophores within the various pattern regions. Specifically, (1) chromatophores were differentialy distributed among pattern regions, (2) greater complexity of gross disruptive patterning had greater underlying melanophores densities, (3) there were significant density differences among non-sib individual animals, among fertilization, and among shipment batches, but not among full-sibs, and (4)kandiyohi individuals had more while burnsi individuals had fewer total melanophores than wild type. A stellate morphology was significantly correlated with high melanophore density, although the relationship of melanophore density to melanophore morphology differed among pattern regions and among genotypes. The functional interrelationships of density and morphology, and their role in disruptive patterning and coloration, are discussed.

Notes: The male rotifer copulatory organ is composed of a urethral canal extending from the tip of the copulatory organ internally to a layer of microvilli. The microvilli project from two different cell types, referred to as the internal and peripheral microvillar cells according to their location. At this microvillar junction a second canal, the vas deferens, continues posteriorly and enters the sperm duct region of the testis. The channel of the vas deferens is formed from the inner wall of three separate cells; the cap, intermediate and basal cells. Peripheral to these cells and parallel to them for their entire length, cross sections of seven prostate gland cells can be observed. Anteriorly, these gland cells are connected to the basal end of the microvillar layer via a short neck region, through which glandular secretion occurs only during copulation. The mechanism of secretion appears to be a form of exocytosis whereby the secretory granule membrane fuses with the cell plasmalemma so that rupturing at the point of fusion will release the granule content into the neck region.The prostate gland cells contain an abundance of autophagic vacuoles while most of the other cells of the copulatory organ contain primary lysosomes and cytolosomes. These organelles may be associated with the aging process in rotifers, or, as in the case of the prostate gland-autophagic vacuoles, with a fast organelle turnover during secretion.

Notes: Spermatogonia of the nine-banded armadillo, Dasypus novemcinctus mexicanus, were studied morphologically using light and electron microscopy and examined histochemically using light microscopy. Immature flat type spermatogonia have ovoid or irregular nuclei with loosely condensed chromatin. Free ribosomes are abundant while profiles of rough endoplasmic reticulum are scarce. Smooth endoplasmic reticulum is a prominent feature occasionally taking an unusual cylindrical form. Mature spermatogonia exhibit rounder nuclei with greater degrees of chromatin clumping. Smooth endoplasmic reticulum is no longer prominent whereas profiles of rough endoplasmic reticulum are quite common. Occasional lysosomal configurations are found in mature spermatogonia.The majority of spermatogonial cells exhibit weak to moderate reactivity when stained with the periodic acid-Schiff (PAS) reaction. Certain cells in each tubular cross section stain vividly with this reaction and the PAS positivity is removable with salivary amylase. Because of nuclear characteristics, position of the cell immediately upon the basal lamina, intensity of the PAS reaction and the relative paucity of the vividly staining cells, it is suggested that they are members of the immature spermatogonial cell line, perhaps acting as stem cells. None of the several other histochemical procedures employed was capable of selectively demonstrating these cells.

Notes: The duodenal glands of four marsupial species, the kangaroo, native cat, marsupial mouse, and bandicoot, form a narrow lobular collar immediately distal to the gastrointestinal junction. In two species, the koala and wombat, the duodenal glands are diffuse and scattered along the intestinal tract distal to the gastrointestinal junction for considerable distances. The glands of all species examined empty independently into the intestinal lumen. Histochemical studies indicate that the latter two species, the koala and wombat, elaborate an acid mucin whereas the former species produce a neutral mucosubstance. Ultrastructural examination shows that generally the duodenal glands are comprised of large pyramidal cells that show a definite polarity, with basally-placed nuclei and apically-situated secretory granules. Species differences, with regard both to the morphology and nature of the secretory granules and to the proportions of cell organelles, exist. The diversity of diet between species is discussed.

Notes: Cytodifferentiation of the myoepithelial cells (MEC) of the rat submandibular gland (SMG) was observed by studying the prenatal and postnatal development of the gland in vivo and in vitro by light and electron microscopy. The anlage of the SMG first appeared on the fourteenth day of gestation and, from its earliest inception, was surrounded by an intact basal lamina. Presumptive myoepithelial cells were first seen at 18 days of gestation coinciding with the onset of secretion in the rudiment. These cells were flattened, peripherally located and subjacent to the epithelial basal lamina. Initial deposition of cytofilaments in the MEC's was observed during the first three days following birth and fully matured cells were seen as early as one week after birth. Presumptive and immature MEC's were observed undergoing mitosis, but once cytofilament deposition had begun in the cells they did not divide. Myoepithelium developed in relation to embryonic secretory structures and were only observed surounding acini and intercalated ducts in the adult gland. New myoepithelial cells were formed as long as new acinar-intercalated duct units were formed. Myoepithelial cells did not produce secretory type granules at any time during their development or in their mature state.Development of the MEC's in vitro paralleled that in vivo and supported the above observations.

Notes: Larval compound (jointed) setae of the polychaete Nereis vexillosa Grube were examined by scanning and transmission electron microscopy and by polarization microscopy. Long-bladed spinigers and short-bladed falcigers are described. The proximal shaft of each of these types of setae flares distally into a serrated collar and encloses the proximal end of a toothed blade. The collar projects on one side as a boss. The blade and the cortex of the shaft have longitudinal channels. A large excentric cavity in the shaft (the medullary channel) contains a loose meshwork of trabeculae. In the distal part of the shaft these trabeculae are aggregated into diaphragms. The seta is invested with an electron dense layer of enamel. Juvenile setae contain both chitin and protein. With respect to the long axis of the seta, the blade and the cortex of the shaft are positively birefringent and the medullary diaphragms are negatively birefringent. KOH extraction renders the setae negative to a test for protein and reverses the sign of birefringence of the cortical material of the shaft.

Notes: The marine priapulid Priapulus caudatus has a voluminous body cavity filled with a blood-like fluid containing erythrocytes and leucocytes (amoebocytes). The hematocrit of animals weighing 0.5-14 gm was 2-10%. The erythrocytes contain a hemerythrin blood pigment. The structure of the coelomocytes was studied by light and electron microscopy. The erythrocytes are nucleated and contain marginal bands, vacuoles and occasionally crystals. The cytoplasm has few organelles. The leucocytes are amoeboid motile cells, the cytoplasm of which contains numerous organelles. The most conspicuous of these are oval particles, probably representing developmental stages of lysosomes. Most of these organelles contain tubules stretching from one pole to another. In the hind part of the animal, certain tissues, primarily the posterior warts contain large numbers of coelomocytes. The histological picture is complicated, showing some resemblance to the lymphoepithelial tissues of vertebrates.

Notes: The dissected tooth bearing bones of 20 specimens of Amia calva (Pisces:Holostei) ranging from the third to tenth season have been examined radiographically and in alizarin red S stained and cleared specimens. Although forms of alternate (1:1) tooth series replacement (sensu Edmund, '60) were frequently observed, even in the youngest, immature specimens, many examples of irregular replacement were recorded. In several bones, the maxillae in particular, series with every third (2:1) or fourth (3:1) tooth replacing were seen and possible patterns of 2:2, were recorded. It is concluded that these data are not consistent with the Zahnreihen concept but support a morphogenic field concept of tooth development.

Notes: The first description of vertebral development in a plethodontid salamander is presented. Eurycea bislineata has larvae that hatch at a rather early stage of development. Somites and the notochord appear early. Somitic differentiation is slight, and no distinct sclerotome can be found. As a result, there is no clear primary segmentation of the skeletogenous tissue. No evidence of a sclerocoele can be found. The amount of sclerotomal cells surrounding the notochord is very low, relative to other tetrapods. Yet discrete perichordal rings of cells do form, in nearly midsegmental positions, and these give rise to the intervertebral cartilages. Osteogenesis of the centra is initiated prior to hatching and is coincidental with ossification of the neural arch. There is no sign of a neurocentral suture. The centrum forms as a thin shell of bone directly from sclerotomal cells. The notochord is a prominent feature of the vertebral column throughout life, retaining its integrity until late in life when some disintegration occurs locally. The notochord is filled with cartilage midvertebrally in late larval stages, and some additional cartilage forms later in life. The intervertebral cartilage enlarges greatly in late larval life. An opisthocoelous joint forms in this cartilage, apparently as a result of differential changes in the cells of the perichordal ring rather than by an invasion of cells from an external source. The intervertebral cartilage is a dominant structural and highly important functional feature of the adult vertebra. In metamorphosed individuals it may become extensively mineralized, and it consists of many different structural kinds of cartilage.The cranio-vertebral joint seems to form in a single segment, contrary to the condition reported by some early investigators. It is complex, and consists of articulations between the odontoid process of the atlas and the occipital arch, as well as between the occipital condyles and atlantal cotyles. The notochord plays a dominant role in the early development of the odontoid, but then changes radically and is absent in the adult process.The anterior trunk region seems to be much more conservative than posterior parts of the column. The patterns of nerve routes and nature of development of the ribs and rib bearers differs greatly from conditions elsewhere in the column. The rib patterns are similar to presumed ancestral conditions. Rib development on the sacral and caudosacral vertebrae is in some ways more similar to that of the anterior vertebrae than of the central trunk vertebrae.Quantitative aspects of variation in the vertebrae of adult salamanders are presented. There is more regional variation and less site variation than would be expected from literature reports.Evolutionary aspects of the origin of the cranio-vertebral joint, transverse process and ribs, patterns of segmentation, and centrum development are considered in the light of the new information on Eurycea. There is no evidence that more than one vertebra is involved developmentally or evolutionarily in the cranio-vertebral joint. The most generalized condition of rib bearers in living salamanders is one in which the dorsal and ventral bearers are in cartilaginous continuity during development. There are many variations on this theme in living species. It is inappropriate to speak of a resegmentation of the sclerotome in Eurycca, even though the adult vertebra is a transsegmental structure, because there is no primary segmentation of the scanty sclerotome. The important feature found in vertebral development in all tetrapods is the perichordal tube and its subsequent differentiation. Questinos concerning precise homologies of the salamander vertebral centrum with those of other vertebrates cannot be answered by data from development sequences with currently used criteria of homology. On the other hand, it appears that all centra, regardless of subdivision, are homologous in all tetrapods.

Notes: The Oberhautchen of scales from the dorsal, parietal, and ventral regions of Sceloporus occidentalis (Iguanidae), Gerrhonotus multicarinatus (Anguinidae), and Anniella pulchra (Anniellidae) were examined with a scanning electron microscope. At low magnification, all scales of S. occidentalis exhibit well-defined outlines of cells belonging to the Oberhautchen layer and the previously overlying clear layer. The dorsal and parietal cells of this species exhibit a minutely dentate Oberhautchen that forms tooth-like spinules 0.2 to 0.5 μ long and arranged in irregular rows. Minute pits 0.1 to 0.3 μ in diameter characterize the Oberhautchen of a ventral scale.Cell outlines are not evident on the scales of G. multicarinatus. The Oberhautchen of dorsal and parietal scales of this species is prominently laminated. Laminae are less prominent on scales of the lateral fold, and no intrinsic surface structure is evident on a ventral scale. In contrast, the fossorial anguinomorph Anniella pulchra exhibits Oberhautchen surfaces with practically no intrinsic microornamentation. However, what appear to be outlines of Oberhautchen cells are visible on the dorsal and ventral scales.These observations suggest that modifications of Oberhautchen microornamentation may have evolved to reduce friction with the substrate or other scales. The lack of pronounced microornamentation of the Oberhautchen on some body scales may indicate that a complex interdigitation between clear layer and Oberhautchen cells is not essential to the sloughing process.

Notes: Stolonic growth has been compared among several genera of calyptoblastic (Campanularia flexuosa, C. calceolifera, Gonothyraea and Sertularia) and gymnoblastic (Pennaria, Bougainvillia, Eudendrium and Cordylophora) hydroids with respect to such features as the (1) complexity and uniformity of the tip movements, (2) constancy of growth cycle duration, (3) variability in growth among cycles, (4) growth rate, and (5) variability of retractions among cycles.The “growth cycle,” previously described in C. flexuosa, is the basis for elongation in all species observed. Its pattern is indistinguishable between the Campanularia species; however, at the generic level the tip movements show peculiarities which delineate each genus from all others. In addition, the movements in all calyptoblasts are uniform from cycle to cycle and comparatively simple, whereas those of the gymnoblasts are complicated by the variable appearance of one or more secondary forward thrusts between crests.A dichotomy is seen between the calyptoblasts and most gymnoblasts in other respects as well. Cycle time is very predictable and cycle-to-cycle variability in growth is relatively narrow in all calyptoblasts. However, in most gymnoblasts both features are much more loosely regulated: only Pennaria shows some degree of control to its timing mechanism, and only in Bougainvillia and Eudendrium does the uniformity of growth per cycle reach the calyptoblast level.On the premise that calyptoblasts are evolutionarily the more advanced group, simplicity and regularity of growth movements are concluded to be the evolved, and complexity and variability the primitive, conditions. On this basis the evolutionary relations among the four gymnoblasts, as deduced from their stolonic growth behavior alone, are consistent in many but not all respects with those interpreted from morphological considerations.

Notes: In order to clarify the morphology of the circulatory system of amphioxus the blood vessels were investigated using modern techniques of light and electron microscopy.The pattern of circulation in amphioxus is forward ventrally and backwards dorsally. In addition, circulating corpuscles, usually associated with the blood of higher chordates, are absent.The circulatory system of amphioxus consists of well defined contractile vessels and vascular spaces or sinuses within a connective tissue matrix. The contractile vessels have a discontinuous endothelial lining resting on a basal lamina and are enclosed by a simple layer of contractile myoepithelial cells. Discontinuous endothelial linings occur throughout the vascular tree, including major and minor afferent and efferent vessels and blood sinuses. This is in contrast to higher animals where the endothelium forms a more or less continuous lining along the inner surface of the boundary layer.It is suggested that the endothelial cells of amphioxus, like the endothelial cells in capillaries of higher chordates, most likely play a role in the physiology of the circulatory system by removing residues of filtration from the basal lamina, thereby facilitating an exchange of materials to and from the surrounding tissues.

Notes: The development of the polarity and bilateral asymmetry of the future adult zooid has been traced to their earliest morphological expression in the palleal bud of Botryllus. The account is based upon continued observation of living buds. The polarized antero-posterior and dorso-ventral axes are first expressed by the skewing of a symmetrical, hemispherical bud towards the anterior end of the parental bud. Identification of these axes is reinforced by the development of a loop-like blood circulation, the primary circulation, in the horizontal plane during the enlargement of the skewed hemisphere to form a stalked vesicle. Bilateral asymmetry is first expressed by the asymmetrical expansion of the vesicle stage. The right posterior corner of the vesicle expands further posteriorly and becomes more acute than the left posterior corner. This larger expansion persists throughout the development of the right atrial cavity, which finally expands across the mid-line to partially surround the gut. The bilateral asymmetry, expressed in the expanded vesicle, is reinforced by the development in sequence of a rounded gut rudiment and a pericardial rudiment in positions that would be expected from the asymmetry of the expanded vesicle. The first appearance of the gut rudiment occurs earlier than had been recognized previously. Conflicting accounts of the time and mode of formation of the pericardial rudiment have been clarified. The results of this study are discussed in the context of determination of bud territory, polarity and bilateral asymmetry.

Notes: Four glands of the house sparrow, chicken and turkey were examined histologically and for their content of amylase. These were the external and intermediate mandibular glands, the maxillary gland and glandula anguli oris of the sparrow and the anterior and posterior mandibular, maxillary and anguli oris glands of the chicken and turkey. Amylase was determined by a starch substrate slide method and by biochemical assay. General morphology and mucopolysaccharide staining are described.All four glands of the sparrow demonstrated significant amylolytic activity by the assay. In the external mandibular and anguli oris glands this activity could be traced to mucous and seromucous cells of origin by means of the starch substrate slide procedure. None of the glands of the chicken or turkey displayed significant amylolytic activity.

Notes: The distribution of monoamine (catecholamine and 5-hydroxytryptamine)-containing nerve cell bodies in the brain stem and hypothalmus of the frog (Rana temporaria) was investigated with the help of the histofluorescence technique of Falck and Hillarp ('62). At the level of the hypothalmus of this amphibian brain, catecholamine-containing nerve cell bodies are found mainly within three areas of the periventricular gray substance, namely the peroptic recess organ, the paraventricular organ and the lateral recess region. On the other hand, most of the 5-hydroxytryptamine (serotonin)-containing nerve cell bodies of the brain stem of Rana temporaria appear to be concentrated within the midbrain tegmentum. This huge mesencephalic nerve cell collection can be subdivided into medial and lateral groups. More caudally, at the level of the isthmic tegmentum, another group of 5-hydroxytryptamine-containing perikarya located close to the midline, within the so-called raphae region, is clearly outlined. The latter group of neurons extends caudally as far as the level of the medulla oblongata. In addition, a small group of catecholamine-containing nerve cell bodies is also found in the ventromedial portion of the rostral midbrain tegmentum, whereas a few other catecholamine type neurons are scattered throughout the lower brain stem of the frog and more especially near the ependymal wall of the fourth ventricle. As a whole, the 5-hydroxytryptamine-containing neuronal systems of the brain stem of Rana temporaria are much more elaborated than the catecholamine neuronal systems of the same structure.

Notes: The guinea pig soleus muscle is a convenient model for the study of slow-twitch intermediate (STI) fiber ultrastructure because it is composed entirely of fibers of this class. Such fibers were compared with fast-twitch red (FTR) and fast-twitch white (FTW) fibers from the vastus lateralis muscle.FTW fibers are characterized by small, sparse mitochondria, a narrow Z line and, an extensive sarcoplasmic reticulum arranged primarily in longitudinal profiles at the A band and with numerous expansions at the I band. Abundant mitochondria with a dense matrix and subsarcolemmal and perinuclear aggregations are typical of FTR fibers. These fibers contain a plexus of sarcoplasmic reticulum at the A band and a less extensive network at the I band. The Z lines are wider (890 ± 74 Å) than those of FTW fibers (582 ± 62 Å). STI intermediate fibers are distinguished from other types by wide Z lines (1205 ± 58 Å), a faint M band, and a less extensive sarcoplasmic reticulum. Compared to FTR fibers, STI fiber mitochondria are usually smaller with less notable subsarcolemmal accumulations.FTW fibers have a more limited capillary supply, rarely contain lipid inclusions, and thus may be restricted to phasic activity. Extensive capillarity, mitochondrial and lipid context, and fast contraction times indicate possible phasic and tonic roles for FTR fibers. STI fibers, characterized by numerous lipid inclusions, extensive capillarity, relatively numerous mitochondria, but slow contraction-relaxation cycles, are morphologically suited for tonic muscle activity.

Notes: The haemocytes of Calpodes ethlius are described with the light and electron microscopes. Five fine structurally distinct types are distinguishable. However only three of these, the granular haemocytes, sphaerule cells and oenocytoids can be positively identified using a series of histochemical stains on smears and on thick sections of araldite-embedded material. The classification is based entirely on the structural features even though several suggestions concerning their function can be made from their fine structure. Intermediates having features of more than one cell type suggest developmental relationships.

Notes: Four hemocyte types have been identified in the late last larval instar of Galleria mellonella. Plasmatocytoids are round to spindle shaped cells, 10-20 μ long and 5-10 μ wide. The cytoplasm contains no distinguishing inclusions. Golgi complexes, rough endoplasmic reticulum and free ribosomes are abundant. Granular hemocytes are oval shaped cells, 10-20 μ long and 5-10 μ wide. The granules, their most characteristic feature, have a diameter of 0.2 μ, a microtubular sub-structure, and are made up of acidic mucosubstances. Lipid droplets may be present in these cells at some stage of development. These cells appear to be phagocytic. Spherule cells are oval shaped, 15-20 μ long and 5-10 μ wide. The spherules, approximately 2 μ in diameter, have a highly ordered substructure and are made up of acidic mucosubstances. Oenocytoids are the largest cells, 20 by 40 μ. The cytoplasm contains mostly free ribosomes and microtubules.

Notes: The epineurium of the esophageal complex of the gastropod pulmonate Triodopsis divesta was examined by electron microscopy. The epineurium consists of two main regions: an inner dense fibrous region adjacent to the avascular neural tissue of the ganglion and an outer cellular region comprised of a variety of cell types embedded in a connective tissue matrix. The dense fibrous region contains smooth muscle cells and associated nerve processes and is invested on the neural side by thin processes of glial cells. The outer highly cellular region contains smooth muscle cells, nerve processes, wandering cells (amebocytes), globular cells, and myoepithelial cells comprising the walls of the vascular system. In addition, a cell type not previously identified in other gastropod epineuria is present. These cells resemble neurosecretory cells. The morphology and structural interrelationships of these various constituents are presented and the possible functions of individual cell types and the epineurium in general are discussed in relation to information available on other molluscs.

Notes: The muscles of the head, neck and thorax of the adult cabbage looper Trichoplusia ni are described for the first time. They are compared to those of Choristoneura fumiferana, Manduca sexta, Smerinthus geminatus, Antheraea polyphemus, Sphinx convolvuli, Crymodes devastator, and Danaus plexippus.

Notes: A precise sequence of four morphological stages of head regeneration in the planarian Dugesia tigrina has been determined by light and electron microscopy. Each stage is identified by a particular morphogenetic process: I, wound healing; II, blastema development; III, growth; IV, differentiation. A wound epidermis consisting of a thin, sheet-like layer of cells, rapidly forms from undamaged epidermal cells at the wound margin. The early blastema is comprised of neoblasts which mature into regeneration cells. The maturational changes include the appearance of a nucleolus, nuclear pores, and perinuclear dense aggregates of granulofibrillar material in these cells. These elements are not evident in the neoblasts of the younger blastema. No mitotic cells are encountered in the blastema or wound epidermis. Cytoplasmic expansion of the regeneration cells is correlated with the formation of numerous microtubules radiating from a juxtanuclear centrosphere. During differentiation of muscle cells, distended, granule-studded cisternae, having moderately fibrillar contents, are regularly disposed adjacent to small patches of myofilaments. Presumptive epidermal cells are recognized by prominent “islands” of finely fibrillar cytoplasm. These cytoplasmic zones persist for a time during definitive differentiation when Golgi bodies, vacuoles, mucous droplets, and rhabdites become evident. The newly formed epidermal cells become inserted among the cells of the wound epidermis. Thus, cells of both the blastema and of the wound epidermis contribute to the reconstituted epidermis.

Notes: Five different kinds of sense organs have been identified on the antennal flagellum of males of Ptilocerembia sp: (1) tactile hairs, (2) thick-walled chemoreceptors, (3) chemoreceptors with thick walls and many pores, (4) thin-walled chemoreceptors and (5) campaniform sense organs. The third type has not been reported previously for other species of insects and combines the characteristics of typical thick-walled and thin-walled chemoreceptors. The campaniform sense organs are situated in sets of three, 120° apart, on the periphery of the distal end of nearly every subsegment. They lie at the transition zone where the thicker cuticle of the subsegment changes to the thin membrane between subsegments.

Notes: The paddlefish (Polyodon spathula) is one of the most primitive and unique freshwater fishes of North America. It is adapted as a plankton filter-feeder. The wide mouth and greatly expansible pharyngeal cavity allows it to process a large quantity of water. Numerous setiform gillrakers, which operate against the flattened surfaces of the gill arches and opercula, are capable of filtering out small food particles. The abundance of taste buds and mucus secreting cells in the buccal cavity and pharynx probably aids in selecting and entangling the food. The first segment of the stomach is provided with peculiar, large longitudinal rods of fat which may help in selecting food from water by causing occlusion of the small lumen when the striated fibers of the muscularis contract. Teeth, unnecessary for microphagous fishes, are absent in adults.The digestive tube is one of the most complex present in fishes. It has two distinct divisions of the stomach and four distinct divisions of the intestine besides possessing a large caecum. Ciliated epithelial cells occur in many parts of the gut and may be an aid in moving or processing the small items of food.Besides the presence of cilia, other primitive features of the digestive tract include the lack of distinction between the esophagus and stomach, the presence of a spiral valve, and the presence of some of the diffuse pancreatic tissue within the wall of the gut.The numerous Peyer's patches in the wall of much of the intestine may be an immunological response to the heavy parasitic infestation.

Notes: The cranial glands of ten species of turtles were studied by the use of histochemistry applied to serial sections of whole heads. The majority were stenohaline species, but one brackish water form, Malaclemys, was included. The results show that all species have two major orbital glands, an anterior Harderian gland, and a posterior lachrymal gland. The latter is seromucous in all species except Malaclemys terrapin in which the gland shows little evidence or organic secretion. External and medial nasal glands are found in all species studied, and also are seromucous glands. With these reslts, combined with a review of the literature the following conclusions are made. The Harderian gland is by definition the orbital gland opening through the medial surface of the nictitating membrane at or near the anterior canthus. It is of constant occurrence, and histological appearance, probably serving the same function. However, despite much recent study this function remains unknown. The lachrymal gland is defined as the orbital gland which opens through the lateral surface of the nictitating membrane, or medial surface of the lower eyelid, at or near the posterior canthus. It is of variable occurrence, absent in many reptiles, and has a histological structure which is also variable. In the stenohaline species it is apparently involved in organic secretion, while in the brackish water Malaclemys it may be involved in salt secretion, as it is in Cheloniidae. The nasal glands in turtles are probably homologous with the nasal salt glands of lizards and birds, but they do not appear to subserve the same function. In all species of turtles studied the nasal glands are seromucous. They are perhaps involved in the maintenance of the epithelium of the olfactory cavity.

Notes: The dorsal proctodeal wall of the Coturnix contains a gland which is especially well-developed in the sexually active male and which secretes a foamy exudate. This gland has not been recorded in any other genus of birds and appears to be unique to members of the genus Coturnix. On the basis of its location in the adult we have named this gland the proctodeal gland (glandula proctodealis). Structure of the gland does not conform to any curently defined category of glands because it is an aggregate of individual glandular units each of which opens independently into the proctodeal cavity but with the entire structure enclosed by a connective tissue capsule. We have thus characterized it as an aggregate gland. Observations on the arrangement and composition of the fibrous capsule and its intimate relationship to the perimysium of M. sphincter cloacae indicate that release of the secretion probably results from contraction of the cloacal musculature. Preliminary data suggest that development of glandular tissue in the female may be a function of age rather than of androgen sensitivity which characterizes the male gland. It is concluded that the chemical nature of the glandular secretion and its function in the sexually active bird, as based on presently available information, remains unknown.

Notes: Wound healing in the integument of the sea cucumber, Thyone briareus, was studied for up to 50 days after inflicting wide excisional wounds and for 14 days after producing incisional wounds. Rapid re-epithelialization of the wound was effected by the migration of epidermal cells and pigment cells from the periphery of the wound margin. This occurred without apparent evidence of concomitant mitotic activity. Dermal wound healing was completed by the fourteenth day in the incision wounds but occurred very slowly in the broad excision wounds. Morula cells seem to be involved in both epidermal and dermal wound healing, although their precise role is unknown. In excisional wounds the integument was never completely restored to its normal appearance during 50 days of observation.

Notes: The electron microscopy of the epiphysis cerebri of the antarctic seal Leptonychotes weddelli revealed a highly organized organ. The general cytological characteristics of the pinealocytes and the glial cells are described. The capillary blood vessels are the nonfenestrated type. The organ is richly innervated by mainly unmyelinated nerve fibers. Most of the axons end in the inner part of the organ, around vessels, some of them in relation with pinealocytes. The significance of the findings is discussed.

Notes: Cleavage and blastoderm formation in Coelopa frigida are extremely rapid developmental processes. In short (6-7 minutes) successive cell cycles, nuclei multiply and spread out through the egg. The movement seems to be aided by endoplasmic vesicles and cisternae which are in direct contact with the nuclear membrane. The first cells to separate from the egg plasmodium in early superficial cleavage stages are the pole cells.Precursor material from multivesicular bodies forms the pole cell membranes. The primary nuclei from the posterior pole region are removed from the blastoderm by the pole cell segregation. Blastoderm nuclei from the regions adjacent to the posterior pole migrate into the residual periplasm after pole cell segregation has been completed and constitute the blastoderm nuclei in that region of the egg. Nucleoli are not revealed during internal cleavage. They appear in pole cells shortly after their segregation. The generation time of the blastoderm nuclei increases after the twelfth cleavage. Concurrently, nucleoli form in the blastoderm nuclei and permanent cell membranes separate individual blastoderm cells. After blastoderm cells have been separated from each other, they remain in contact with the interior yolk sac by means of cytoplasmic canals. This contact is maintained at least during the early phases of blastokinesis. Observations on nuclear migration and rapid membrane formation are discussed as examples of protein assembly from subunits as an alternative to de novo protein synthesis in early stages of development.

Notes: Ovarian follicular histology of the lizard Anolis carolinensis was studied in relation to follicular size and rank. The structure of the Anolis follicular granulosa is similar to that described in other reptiles. Changes in the granulosa during follicular hypertrophy are also similar to those described in other species. Follicles of low rank in the linear size-gradation exhibited atresia.Counts were made of erythrocytes per millimeter of thecal tissue in crosssections of follicles of different size and rank. Follicles greater than 2.6 mm in diameter exhibited a marked increase in the number of thecal erythrocytes. Also, follicles of a similar diameter tended to possess a greater number of thecal erythrocytes the highter the rank in the linerar size-gradation. These observations support the hypothesis that follicular selection involves appropriation of blood and blood-borne hormones by larger follicles.

Notes: Some of the cytological and histochemical characteristics of hemocytes of Thyropygus poseidon were studied. Jone's system of classification of hemocytes was extended to millipede hemocytes. Seven classes were identified as prohemocytes, plasmatocytes, granular hemocytes, cytocytes, oenocytoids, spherule cells and adipohemocytes. Oenocytoids were rarely found. All cells except prohemocytes and oenocytoids sequestered oxidized products of catechol. Results of the histochemical tests for proteins also suggest that these cells sequester plasma proteins. Cytocytes do not bring about any visible coagulation similar to the hemocytes of some hemipteran insects. Granular hemocytes contain phenol-oxidase capable of oxidising tyrosine as well as catechol, similar to the hemocytes of crustaceans. In this respect millipede hemocytes differ from insect hemocytes. It is suggested that these cell types may represent distinct cell lines and may not represent transformation of one cell type to another.

Notes: Twenty-three stages in the embryonic development of the western painted turtle, Chrysemys picta bellii are described. The staging is based primarily on morphological changes, as well as age and size of the embryo.

Notes: Scanning and transmission electron microscopy were used to investigate the surface area and number per unit area of microvilli from jejunal villus epithelial cells in the rat, hamster and dog.The calculated mean microvillus surface area was 0.419 μ2, 0.573 μ2, 0.751 μ2 for the rat, hamster and dog respectively.The largest number of microvilli per square micron freeze dried villus surface was measured in the rat with a mean value of 65. Hamster and dog freeze dried specimens had lower mean values of 54 and 34 microvilli respectively.The total microvilli surface area in square micron per square micron villus surface was more closely related for the three species with values of 27.23 for the rat, 30.94 for the hamster and 25.53 for the dog.These data indicate an inverse relationship between the mean microvillus surface area and population density in the species studied. However, the total microvilli surface area per unit villus surface is relatively similar for the three species.The observed number of microvilli per unit villus surface was shown to vary depending upon the dehydration technique employed for preparation of scanning electron microscopic specimens. This variation probably reflects shrinkage artifact and should be considered in soft tissue studies involving the scanning electron microscope.

Notes: In Esox americanus and Esox niger (Esocidae) there are two types of surface pits, sensory and nonsensory. Both types of pits are morphologically very similar and are associated with modified (cardioid) scales. The pits are distinguished by the presence and absence respectively of neuromasts. Ultrastructure of the neuromasts indicates that they are basically similar to previously described neuromasts. However, the hair cells have crystalline-like deposits in the nuclear region. The nonsensory pit contains a small group of distinct epidermal cells, called central cells. These cells occupy a central position in the pit, similar to that of the neuromasts in the sensory pit. The central cells are unlike any cell types described for fishes, and on an ultrastructural basis no function can be ascribed to them and the significance of the nonsensory pit is unknown.

Notes: Esox americanus and Esox niger (esocidae) possess two types of surface pits, sensory and nonsensory. The pits are morphologically very similar and both are associated with modified (cardioid) scales. The pits are distinguished by neuromasts in the sensory and central cells in the nonsensory pit.Neuromasts and central cells are responsible for the formation and maintenance of respectively the pit and cardioid scale. This supports an extension of the epidermal co-participation hypothesis that epidermal cells control the form of dermal structures in addition to contributing to composition.The central cells are similar in structure to induced primordial cells of regenerating neuromasts.The development of primordial cells may be arrested and the cells maintained in a static condition during which time they still influence the dermal tissues and maintain a pit and cardioid scale. Essentially this represents the experimental conversion of a sensory pit into a nonsensory pit. This evidence is taken in support of the hypothesis that the nonsensory pit and central cells represent an aplasic condition of the lateral line system.

Notes: The gular gland of the bat Tadarida brasiliensis is a specialized sebaceous gland located in the skin of the suprasternal region of adult males. It consists of an aggregation of simple branched tubulo-acinar gland units, the number of which varies seasonally. Each acinus is composed of densely packed sebaceous cells at various stages of differentiation. Acinar basal cells and cells of the epithelium of the ducts can differentiate into sebaceous cells. Two main changes appear in the cytoplasm concurrent with the sebaceous transformation: the differentiation of cytoplasmic organelles and the deposition of lipid material. The appearance of a different type of mitochondrion and the development of large numbers of ribosomes and polyribosomes can be recognized in the cytoplasm at an early stage of differentiation. Concomitant with the deposition of significant numbers of lipid droplets, the cells develop abundant agranular endoplasmic reticulum occurring mainly as scattered tubular cisternae. These at times form whorls surrounding lipid droplets. At later stages, the cisternae of the agranular endoplasmic reticulum often occur in crystalline arrays between secretory oil droplets. The roles of the different cytoplasmic organelles, especially in relation to the production of sebum, are discussed.

Notes: The mutant gene srn produces sireniform abnormalities in the mouse. The effects of this gene on normal prenatal development were examined histologically by retrograde analysis from day 10 through day 18 of gestation.The sireniformphenotype is characterized by the fusion of the hindlimbs and accompanying defects of the posterior appendicular skeleton. Visceral defects involve the urogenital system and the lower intestinal tract. A single umbilical artery arises from the dorsal aorta and controls the fetal circulatory pathway normally mediated by the lateral umbilical arteries. This artery is believed to have resulted from the fusion of the paired primitive umbilical arteries.It is suggested that the srn mutation causes a narrowing of the posterior amnion early in development. The resulting abnormal pressure causes a dorsal displacement of the hindgut, allowing fusion of the hindlimb buds. Abnormal structural relationships and pressure in the narrowed posteriior region disrupt normal urogenital and intestinal development and increase the proximity of the primitive umbilical arteries.

Notes: The retinofugal projections of the snake Thamnophis sirtalis were studied by the method of experimentally induced Wallerian degeneration stained by the Fink-Heimer method. The retinal ganglion cells project to all parts of the contralateral lateral geniculate complex, nucleus lentiformis mesencephali, nucleus geniculatus pretectalis, nucleus posterodorsalis, basal optic nucleus and superficial layers of the optic tectum. In addition, the retinofugal projections were observed terminating in portions of the ipsilateral lateral geniculate complex and nucleus posterodorsalis.Examination of the morphology of the retinal terminal areas stained for Nissl substance with cresyl violet led to the conclusion that these regions are well differentiated and should not be considered poorly developed when compared with other reptilian forms such as turtles.

Notes: The course of the statoblast formation in Pectinatella gelatinosa was divided into four stages and studied histologically and histochemically. The bottom of the cystigenous cup is a center of cystigenous cell differentiation and the peripheral zone of the inner cystigenous layer turns to the outer cystigenous layer as the cystigenous cup grows. The annulus is formed by migration and transformation of the outer cystigenous cells.During early stages, the yolk cells have an intensely pyroninophilic or RNA-rich cytoplasm. The cytoplasmic pyroninophilia then diminishes as the amount of yolk granules increases.Several kinds of yolk substances occur in the mature statoblast. During statoblast formation glycogen appears first, then glycoprotein and finally neutral unsaturated lipid.Acid phosphatase activity is associated with granular structures in the cytoplasm. In the cystigenous vesicle, acid phosphatase activity is low and confined to the apical extremity of the cell. Histochemically detectable alkaline phosphatase activity is not involved in the formation of the statoblast.

Notes: The anatomy and physiology of feeding in miniature swine were studied, using gross dissection, electromyography, cinematography, and cineradiography.Small particles are preferred for ingestion, and large items are usually broken down outside of the oral cavity. The particles are initially picked up with the lower lip and then retrieved by the tongue; the tongue very rarely leaves the oral cavity. Geniohyoid, mylohyoid and digastric are the most active muscles during food collection.Mastication is fairly rapid (3 cycles/sec) and involves a transverse component which may be either medially or laterally directed. The direction of motion is generally reversed with every chew. Electromyography indicates that the transverse rotation is caused by a force couple consisting of protrusors (masseter, medial and lateral pterygoids) on one side and retrusors (zygomaticomandibularis and temporalis) on the other. The direction of the rotation is not necessarily related to the side containing the bolus. Mandibular depression is electromyographically biphasic. Concurrent tongue and hyoid movements complicate the interpretation of activity patterns in the oral floor.Both masticated food and liquid are stored between the tongue and the soft palate and epiglottis before being swallowed. Swallowing involves very strong activity in all of the hyoid and tongue muscles and very low activity in the adductors. Liquid is taken in by suction rather than lapping.Comparisons with other mammals are presented.

Notes: The wall of the gametolytic gland in Aplysia and Phyllaplysia consists of a muscular layer lined with an epithelium incorporating four distinct cell types, some of which show intense secretory activity. The cytoplasm of these cells, rich in RNA, has a peripheral layer of densely-packed mitochondria in association with a smooth endoplasmic reticulum. Lipid globules, perhaps resulting from absorption of lumen contents by microvilli, appear in the cytoplasm in the course of growth and reproductive activity. A basal band of fibrillar material appears to serve as a cytoplasmic skeleton. The elaboration of cell types, extensive areas of cytoplasmic RNA, and vigorous secretory activity suggest important roles for this organ such as development of food reserves, recycling of sexual materials of high physiological value, and interaction with the bag cells of the nervous system in coordinating ovulation with the availability of capacitated, exogenous sperm.

Notes: The predaceous neotropical characoid fish Ctenolucius has an essentially homodont dentition, the number of teeth increasing linearly with age. The basic manner of tooth replacement suggests that Ctenolucius is a primitive characoid. Tooth replacement continues throughout life and is similar to that of tetrapods, involving replacement waves which pass from the back to the front of the jaws. The waves containing the greatest number of teeth are found just anterior to the middle of the jaws. In the upper jaw the increase in the number of teeth is restricted to the anterior portion (premaxillary) whereas the number on the posterior part (maxillary) remains constant. In specimens measuring from 68-230 mm in standard length the posterior portion of the upper jaw doubles in length whereas the anterior portion triples. It is suggested that the area immediately anterior to the middle of the jaw, where replacement waves are longest, is where most of the increase in tooth numbers occurs.During growth of the teeth the absolute height is always greater than the absolute width as the shape changes. The final shape of the recurved conical teeth is determined only in the last stages of tooth formation when the main axis of growth abruptly changes.

Notes: Improved histological procedures have revealed in some detail the form and structure of auditory receptor organs in the frog. These organs, the papilla amphibiorum and papilla basilaris, are located in extensions of the saccular cavity, and lie in a path of vibratory fluid motion beginning at the columellar footplate and extending in a continuous circuit through the perilymph spaces and the round window back to the middle ear region.These organs exhibit great uniformity, and for the amphibian papilla there is a high degree of complexity in the tectorial structures that overlay the ciliated ends of the hair cells. In both papillae a “sensing membrane,” which is a derivative of the tectorial body, lies in the path of fluid flow and aids in the stimulation process.The mode of stimulation of the hair cells in the amphibian ear is peculiar, and in principle is the reverse of the familiar one of reptiles, birds, and mammals.

Notes: To determine the prism sheath configurations in human cuspal enamel 80 teeth were initially ground to produce flat surfaces through the following planes: a horizontal series at successively greater distances from the dentinoenamel junction and longitudinally through the center of the cusps. Individual teeth were suspended in an acid-alcohol solution (1 cm3 conc. HCl in 100 cm3 95% ethanol) at 37°C for seven to ten days. The treatment “softened” the enamel to a depth of approximately 1 mm. The teeth were embedded in Epon and sectioned at 0.5 to 10 μm with a diamond knife. Thick and thin ground sections for phase contrast microscopy and acid-etched ground sections for Nomarski differential interference microscopy were prepared through the same regions. In thicker longitudinal sections, the prisms in gnarled enamel formed a zig-zag pattern which was unlike the twisting pattern generally observed in ground sections. The thinnest transverse sections showed the sheath outlines to be dramatically different from those seen elsewhere in the enamel. Some prism sheaths were circular, others were in the form of spirals. What could be described as sheaths within sheaths were also seen. In the thinnest longitudinal sections the prisms were seen to be elongated and discontinuous. Sheath outlines in enamel adjacent to the central core of gnarled enamel were similar to those described elsewhere in the body of the enamel. Keyhole, modified keyhole patterns and arcade forms were the dominant sheath patterns. Other atypical sheath configurations were seen scattered throughout this region.

Notes: The differentiation and degeneration of the cement gland in Xenopus laevis is described. The gland is first observed histologically at stage 19 (neural tube stage) as a packed group of apical ectoderm cells heavily laden with oocyte pigment granules, lying ventral to the cranial neural fold. By tailbud stage 35/36, the gland cells have increased in height and are approximately ten times taller than nonglandular apical ectoderm cells. The nuclei divide the gland cells into an apical region that is eosinophilic and contains oocyte pigment granules, and a basal region that contains clear droplets. The cells are decreasing in height by stage 40 (early tadpole) and begin to lose their pigment granules. Between stages 45 and 48, the pigment is extruded and the clear basal droplets diminish in number. From stage 48 to 49 the cells become vacuolated and the histotypic characteristics of the functional gland are lost. The gland is not vascularized, nor do phagocytic cells appear in its vicinity during any stage of its development. It remains bordered at its base by subjacent basal ectoderm during its entire life cycle of 10 to 12 days at room temperature.

Notes: Fibrosis and lymphocytosis are common in aflatoxin-induced hepatoma in rainbow trout. It is suggested that these reactions may control the growth of tumors and in some cases destroy them. Nearly all of the hepatomas we have observed are fibrotic to some extent. The extent of the fibrosis seems to be age dependent and in advanced cases fibrosis appears to have disorganized the tumors to a degree which we believe is suppressive. The lymphocytosis shows a negative correlation with the size and age of the hepatoma, being found almost exclusively in the very “early” (small) hepatomas and preneoplastic nodules. It is suggested that the invasion of the tumors by lymphocytes is a host defense mechanism.

Notes: Using the electron microscope, two types of smooth muscle cell have been recognized in the upper urinary tract of the pig. One type is confined solely to the renal attachment of each minor calix and possesses a number of atypical features. These cells are not grouped into bundles but form a loose meshwork. They frequently branch, are comparatively long with very irregular profiles, and are separated by relatively large amounts of connective tissue although maculae adhaerentes are occasionally observed between neighbouring cells. Dense micronbrils occur in the vicinity of the cells which are surrounded by a partial basal lamina. Groups of axons are seen in the region, many of which contain small dense-cored vesicles. Within the atypical cells, filaments are loosely packed and accumulations of micropinocytotic vesicles are not observed. These features contrast markedly with those of typical muscle cells in other regions of the upper urinary tract where they form tightly packed bundles unrelated to axon profiles. The typical smooth muscle cells are larger and more regular in outline, are surrounded by a complete basal lamina, possess tightly packed filaments, and contain numerous micropinocytotic vesicles and glycogen particles.Similar modified muscle cells occur in the unicaliceal systems of other species where they are also confined to the proximal end of the urinary tract. It is suggested that the atypical cells are specially adapted to function as spontaneously active “pacemakers” initiating ureteric peristalsis.

Notes: After perfusion of the animals with buffered aldehyde solutions, spinal cords of normal dogs, cats and monkeys were prepared for electron microscopic examination by standard methods. Observations were limited to the upper cervical levels in all animals, except in two cats where thoracic and lumbar regions also were studied. Large mitochondria, up to 5.0 μ in diameter, are abundant in astrocytes that form a dorsolateral glial septum in dogs and cats. The septum is present but less well developed in monkeys and the accompanying large mitochondria are smaller and less numerous. These mitochondria have a moderately dense matrix and few or no cristae. They are accompanied by more numerous smaller mitochondria with similar matrix and prismatic cristae. The cristae are of constant size and shape in all three species but vary greatly in numbers and arrangement. It is suggested that local mechanical forces may be responsible for the configuration of these morphologically specialized mitochondria.

Notes: Electron microscopic examination of developing myofibrils in regenerating skeletal muscle of Rana pipiens tadpole tails reveals that sarcoplasmic reticulum (SR) is in regular and close association with Z-lines of young sarcomeres before transverse tubules have formed alongside the myofibrils. SR is also associated with M-lines of young sarcomeres but on a less regular basis than with Z-lines. Counts of the number of contact sites of SR with Z-lines, M-lines and combined A- and I-bands of longitudinally sectioned sarcomeres of young myofibrils confirms the visual impression that the SR associates with a relatively much greater frequency with Z-lines and M-lines than with other regions of the sarcomere. This suggests the formation of a specific bond between SR and Z- and M-lines.Serial transverse sections of developing myofibrils were examined in order to determine whether Z-lines displayed SR association at all stages in their formation. Of fifty discrete Z-lines that were examined, only four smaller Z-lines appeared to lack SR association. An examination of a comparable number of more diffuse Z-bodies representing an earlier stage of Z-line formation suggests that no more than one-half of these Z-bodies were accompanied by SR. These observations support the conclusion that SR does not initiate formation of Z-line precursor elements, but rather associates with Z-lines as they condense from more diffuse Z-bodies.

Notes: An intensive search has failed to locate a proximal centriole in the neck of the rat spermatozoon. This centriole is present in late spermatids but disappears before spermiation. The distal centriole also degenerates during spermiogenesis, though more gradually; it is no longer demonstrable by the time the spermatozoa reach the cauda epididymidis (except as a few remnants in a small minority of the cells). The rat spermatozoon is thus exceptional among mammals in being effectively acentriolate. The implications of this are discussed. Since there are no centrioles, the activity and control of the flagellum cannot depend on a centriole as a kinetic center. Furthermore, since no centrioles are introduced by the rat spermatozoon at fertilization, there can be no paternal inheritance of a formed centriole through the cytoplasm. And, in this species at least, paternal centrioles have no role in the first cleavage of the fertilized egg.

Notes: The spatial distribution of collagen loss in syngeneic grafts of skin was studied autoradiographically. Grafts of radioactive skin from rats that were chronically injected with 14C- or 3H-proline were placed onto unlabeled inbred rats. These radioactive skin grafts were removed at 0, 2, 4, 8 and 20 weeks after grafting, and observed both for distribution of isotope, as determined by autoradiography, and histological changes. Since 91% of the total radioactivity in the skin resided in collagen, the autoradiographs were specific for collagen.Thick full-thickness and split-thickness grafts showed a zonal loss of radioactivity, with isotope being lost most rapidly in the subepidermal region. Collagen newly formed in this area resembled scar collagen.Thin full-thickness grafts did not show a zonal reduction of isotope, but instead lost radioactivity in a diffuse manner. The newly synthesized collagen bundles of the thin full-thickness grafts were similar in thickness to the collagen bundles of control skin, but did not form the lattice network seen in the controls.Autoradiographic losses and histological changes are related to the biochemical quantification of collagen turnover, to scar formation, and to the cellular control of collagen mass in skin grafts.

Notes: In rats, a portion of Meckel's cartilage  -  that lying within the mandible but proximal to the rostral convergence of the bars  -  gives rise to no definitive structures. It offers especially favorable opportunity to study cartilage resorption. By the eighteenth fetal day it is established as a hyaline cartilage bar, and a thin perichondral bone shell starts to form on its lateral aspect, completing encirclement in the next two days. On day 19 cartilage within this bone shows chondrocyte hypertrophy, lacunar enlargement, and matrix calcification. Osteoclasts open a fenestra laterally in the bone and commence removal of calcified cartilage matrix. The erosion front expands rapidly, moving medially (preceded by cartilage hypertrophy and calcification) and extending proximally and distally along the segment. Chondroclasts (multinucleated cells identical with osteoclasts) dominate the erosion front. Capillaries and various mononucleated cells follow. Bone formation is much delayed except in the most rostral extremity, so that, contrary to the situation in endochondral osteogenesis, one is examining calcified cartilage resorption in uncomplicated form. This resorption, including the perichondral bone shell, is virtually complete by day 21, and intramembranous bony reorganization of the site is in progress at birth.Several features of chondroclasts, including some in dispute or not easily seen in vivo, are well displayed. These include ameboid form with pseudopodial extensions (sometimes filamentous), and fusion of some released chondrocytes with entering chondroclasts. Osteo/chondroclasts are often found in contact with perichondral bone at one extremity and calcified cartilage elsewhere on the same cell. There is evidence that matrix calcification is prerequisite to the chondroclastic activity.

Notes: Tissue cultures of fetal rat adrenals were used to study the effects of corticosterone on the ACTH-induced ultrastructural differentiation of cortical cells and their mitochondria. Corticosterone in dosages of 0.2, 2.0, 5.0, 10, and 20 μg/ml (corresponding to concentrations of 6 × 10-7, 6 × 10-6, 1.5 × 10-5, 3 × 10-5, and 6 × 10-5 molar) was added alone or together with 100 mU/ml of ACTH to the culture medium, daily from the sixteenth day of cultivation up to and including the twenty-first day. Corticosterone alone induced no ultrastructural changes in cortical cells. Corticosterone in concentrations of 6 × 10-7 to 3 × 10-5 M given with ACTH induced hypertrophy of Golgi apparatus. Corticosterone in concentrations of 6 × 10-5 M inhibited the ACTH-induced differentiation of cortical cells. However, the nuclear chromatin increased and Golgi apparatus was strikingly hypertrophied. Mitochondria often aggregated adjacent to the nuclear envelope but their ultrastructure remained undifferentiated with tubular or tubulovesicular cristae. Ribosomes appeared as single particles. A marked increase of smooth surfaced endoplasmic reticulum was noted also in cortical cells treated with 6 × 10-5 M of corticosterone.The present observations suggest that corticosterone acts as an intracellular inhibitor in cortical cells. It appears to inhibit cytoplasmic protein synthesis at the ribosomal level and prevents synthesis of cytoplasmic mitochondrial protein synthesis stimulating factor and the latter, in turn, inhibits the activation of mitochondrial protein synthesis. A new model is presented to explain the regulation of growth and secretion in the adrenal cortex.

Notes: A method for producing flexible silicone rubber casts of the airways of the lungs in-situ is described. Casts are made to correspond to lung volumes occurring during normal breathing. The lung is prepared for casting by replacing the air within with CO2 followed by filling with degassed physiological saline. The saline dissolves the CO2 gas within the airways allowing for a bubble-free finished cast. Casting compound is then slowly injected through the trachea. The saline diffuses out of the lung and passes out of the thorax through several small slits in the thoracic wall. After the injection is completed, the cast lung is allowed to cure in-situ before it is removed and the tissue digested away. Finished casts have an overall shape corresponding closely to the shape of the thorax. Casts produced by this in-situ method appear to have more realistic geometrical relationships than those produced from excised lungs.

Notes: Injections of posterior pituitary powder induced a significant stimulation of mitotic activity in the zona glomerulosa of intact and hypophysectomized rats. Hypophysectomy depressed this activity. The effect of the powder may be due to the presence of vasopressin.

Notes: The localization of alkaline phosphatase activity during morphogenesis of the thyroid gland was studied at the fine structural level in Holtzman rats from the fifteenth day of foetal life till the first day after birth. The present work deals with the formation of thyroid follicles in the median thyroid primordium only. Since the rat thyroid does not develop synchronously, the three stages described may overlap during a given day of development. In the precolloid stage that extends roughly from the fifteenth to the nineteenth day of development, alkaline phosphatase activity is localized in Golgi saccules and vesicles and also in smooth membrane tubules and vesicles found in the cytoplasm near the lateral plasma membranes. At the end of this stage the lateral plasma membranes become strongly reactive and a cluster of positive vesicles and tubules appears immediately under the junctional zone. The second phase, the early colloid stage (17-19 days), is characterized by the formation of the colloid cavity in center of the disc-like junctional zone: at this moment the newly formed apical plasma membrane bearing the microvilli shows the reaction product. During the third stage (18 days onwards), which starts with a gradual increase in the diameter of follicular lumina, a drastic fall in alkaline phosphatase activity is observed. In one day old rats, follicular cells are completely negative. These findings are briefly discussed in connection with thyroid cell differentiation.

Notes: The total mass of skeletal muscle in male and female mice of strain 129/Re was found by removing the muscle from the bones using papain. The total muscle mass of male and female mice of under three weeks of age was not significantly different. After this time the muscle mass of male mice increased more rapidly and plateaued at a higher value than that of females. However, if the total muscle mass was plotted as a function of body weight then there was no significant difference between males and females. The percentage of body weight taken up by skeletal muscle was the same for males and females at all stages of development.

Notes: Adult male mice fed “ad libitum” were given a single intraperitoneal injection of 35S-sodium sulfate and sacrificed one, three and six hours after. Plastic embedded one micron thick sections from duodenum, jejunum and ileum were radioautographed and the uptake of the 35S by goblet cells was analysed. Goblet cells of the small intestine originate in crypts and migrate to villi reaching their tips where they are released into the intestinal lumen. Radioautographic reaction appeared over all goblet cells whether in the crypts or in the villi indicating continual synthesis of sulfomucins.By determining the silver grain concentration over goblet cells at different levels of crypts and villi it was shown that the cells of duodenum and jejunum become more active in the synthesis of sulfomucin, when they reach the upper half of the villi. In the ileum, although a similar maturation may occur, the results were not statistically significant.

Notes: Previous studies have demonstrated the presence of myoid cells in monolayers derived from cultured testicular fragments. In order to determine if monolayers of myoid cells can also be produced by other types of tissue cultures, monolayers derived from fragments of mouse adrenal capsules, cultured in McCoys modified 5A medium, were examined for the presence of myoid cells. The cells of the resultant monolayers contained numerous free ribosomes and abundant profiles of granular endoplasmic reticulum, as well as 40-60 Å thick filaments and associated dense bodies. In these respects they are identical to myoid cells found in monolayers in testis cultures. Contrary to earlier reports indicating that the adrenal capsule is composed of fibroblasts, this study demonstrates that myoid cells are a major component of the capsule of the rat and mouse adrenal gland.

Notes: The development of the mouse ovarian interstitial tissue was examined by light and electron microscopy at postnatal days 9, 10, 11, 12, and 18. Prior to day 12 the ovarian stroma is composed of fibroblast-like cells. These cells contain rough endoplasmic reticulum, elongate mitochondria with lamellar cristae, and lipid bodies which appear uniformly electron opaque. On postnatal day 12 islands of lipid containing cells are seen deep in the interfollicular stroma. These cells referred to as interstitial cells have rounded mitochondria with tubular cristae, smooth endoplasmic reticulum, lipid bodies with extracted centers, well-developed Golgi complexes, and solitary cilia lacking the central tubular elements. By postnatal day 18 similar cells are seen in the thecal regions of normal appearing follicles. Also seen in the theca are cells whose cytoplasm contains characteristics of both fibroblasts and interstitial cell.It is proposed that the interstitial cells develop from the fibroblast-like stromal cells, that this development proceeds in a wave from deep in the interfollicular tissue toward the follicle, and that the interstitial cells are the source of ovarian steroid production during this period of development.

Notes: The surfaces of palatal shelves from carefully staged A/Jax mouse embryos were examined with the scanning electron microscope prior to and during palatal fusion. No change was observed in the appearance of cells covering the oral and nasal surfaces of the shelves. A change was observed, however, in the region of presumptive fusion, and was detectable on vertical shelves just prior to transposition. This change initially involved surface cells along the future medial edge of the shelf at the level of the second to third rugae. It was characterized by a loss of distinct cellular boundaries, the appearance of intercellular gaps caused by apparent retraction of adjacent cells, and a progressive accumulation of filamentous material at the surface. These alterations spread posteriorly along the medial edge of the shelf during transposition and fusion. While it was impossible to determine the precise nature of the surface change from S.E.M. data alone, the fact that it both preceded closure and was restricted to the region of subsequent contact and fusion between the shelves suggests it may be a prerequisite for normal palatal fusion and may represent an expression of the acquisition of a potential to fuse similar to that proposed for palatal fusion in vitro.

Notes: Unilateral extirpation of the lung in rats is followed by increased mitotic activity in alveolar cells of the contralateral lung, reaching a maximum six to seven days after operation. The response is delayed if the cavity created by the operation is packed with plastic sponge. Unilateral collapse of the lung without removal of tissue also leads to a contralateral mitotic response. Changes in the rate of cell proliferation evidently are not directly dependent on changes in tissue mass and it is suggested that compensatory growth in the lung may be controlled by chemical factors whose local concentration depends on variations in the rate of blood flow.Other changes which follow partial extirpation, observed particularly in the residual tissue of resected lungs, include high rates of proliferation in pleural cells, sub-pleural tissue and bronchial epithelium. It appears that in the regenerating lung new tissue may be formed partly by the proliferation of cells in the main mass of residual tissue and partly by more localized changes in specific tissues.

Notes: The fine structure of the choroid plexus of the immature pig consists of an epithelial layer of cells contiguous with a subepithelial region containing fibrillar elements. The apical surface is extended as numerous digitiform microvilli. At irregular intervals, apical tufts of cilia occur that contain 10-14 cilia with a typical 9+2 subfibrillar arrangement. The cytoplasm is composed of randomly distributed smooth tubular endoplasmic reticulum, apically concentrated cisternae of rough endoplasmic reticulum, Golgi areas, glycogen and numerous mitochondria. Lateral cell membranes are typically tortuous, interdigitating and possess an apical tight junction. Various vesicles are found including pinocytotic vesicles, lipoid inclusions and lysosomes. A comparative ultrastructural study of the choroid plexuses from the lateral, third and fourth ventricles failed to demonstrate significant differences between these structures of different embryological origin.

Notes: The vibrissae of the California sea lion are richly innervated with myelinated fibers that terminate in three distinctly different endings. Large nerve bundles enter the base of the follicle and immediately branch into smaller bundles that traverse the connective tissue trabeculae below the large ring sinus. Some neurons terminate in a lamellated corpuscle in close relationship to the venous sinuses of the proximal cavernous tissues. The remainder of the nerves continue distally parallel to the glassy membrane terminating in two specific types of endings arranged in a ring about the shaft of the vibrissae at the level of the upper portion of the ring sinus. One type of ending is on the outer surface of the glassy membrane where the myelin sheath terminates abruptly and the sensory ending is flattened into a thick, lancet-shaped structure. An extension of cytoplasm from a specialized supportive cell covers this terminal segment of the nerve on two sides, while numerous finger-like extensions protrude into the connective tissue from the narrow, uncovered sides. The second type of ending penetrates the glassy membrane, branches, and terminates in close apposition to the Merkel cells in the outer root sheath. Amyelinated nerves of various sizes are frequently observed in the same bundles as the larger myelinated fibers, but to date, the position of their termination has not been established.

Notes: The B cells of dog pancreatic islets were studied by electron microscopy. The crystalloid core of secretory granules in B cells is unique. The crystallization of the secretory granule core appears to be accomplished in the Golgi apparatus. The square or hexagonal network with a periodicity of 30-60 Å that is produced suggests that the unit cell is either hexagonal or rhombohedral. The electron opaque dots which constitute the periodic densities may represent the insulin molecule itself in a crystalloid array.

Notes: Smooth muscle of the small intestine of the rat was fixed by vascular perfusion employing aldehydes in a balanced salt solution, followed by immersion fixation in aldehydes and post-osmication. In such tissue preparations thick filaments approximating 140 Å in diameter are observed in virtually all the smooth muscle cells. The thick filaments are rather uniformly distributed among the more numerous thin filaments. The nearest neighbor distances between the thick filaments range from 400 to 700 Å. The thick to thin filaments ratio is found to apporximate 1:12. Only thin filaments are observed in the most distal segment of terminal processes of muscle cells and the tips of these processes appear to be lined by attachment plaques. A clear segregation of the thick filaments from both dense bodies and attachment plaques is seen. Distally along the tapering extremities of muscle cells progressively more of the plasma membrane is found lined by attachment plaques. These observations are interpreted as strong evidence that the contractile apparatus of the vertebrate smooth muscle cell consists of interdigitating arrays of thick and thin filaments collated into contractile units by the anchoring of the thin filaments in dense bodies and attachment plaques.

Notes: The adrenergic innervation of the rat submandibular and parotid glands was investigated by monitoring the uptake of H3-NE by nerve terminals with electron microscopic autoradiographic techniques. Both glands contained nerve bundles in the stroma encompassed by a Schwann cell sheath. Silver grains due to H3-NE were observed overlying several nerve terminals found in these nerve bundles, while other nerve terminals in the same bundle were devoid of silver grains. In the submandibular gland, adrenergic nerve terminals characterized by silver grains due to H3-NE were observed in the stroma in close relationship to, but not in direct apposition to parenchymal cells. In the parotid gland, silver grains due to H3-NE were observed overlying nerve terminals contained within the basement lamina and in close contact with acinar cells.

Notes: The present investigation attempts to correlate the appearance of catecholamines to receptor-induced metabolic events (adenyl cyclase-phospho-diesterase) in the developing human heart. Adrenergic innervation, examined with the Falck-Hillarp fluorescence technique as well as by electron microscopy, reveals the presence of catecholamine-containing cells in or near the fetal heart at all ages studied (8-18 weeks). In most instances these cells occur either in association with extrinsic nerves along the aorta and pulmonary trunk or in the interatrial septum. Ultrastructural features of these cells include dense core vesicles. Acetylcholinesterase positive cardiac nerves and ganglion cells are observed. Highest basal activities of adenyl cyclase are found at the sixth fetal week. The enzyme is activated by fluoride ion from the eighth through the seventeenth fetal week, but not by catecholamines. Glucagon stimulates this enzyme at the seventeenth fetal week. Phosphodiesterase activity is progressively increased from the eighth to the seventeenth weeks and is inhibited by aminophylline from the tenth through the fifteenth week. Although catecholamine cells are present in the fetal heart, adrenergic fibers are absent at all ages studied. Failure to observe adrenergic fibers may correlate with the lack of hormonal activation of receptor mechanisms.

Notes: The sympathetic innervation of these ducts was studied by means of the Falck fluorescence histochemical technique and electron microscopy. A loose network of sympathetic fibers was observed on the surface of the lymphatic duct, yet there were large areas of the duct wall void of any fibers. The majority of the fibers branched from the plexuses of sympathetic fibers surrounding the vasa vasorum of the ducts. Sympathectomy experiments demonstrated the fibers do not travel up the vagosympathetic trunk or the carotid artery to reach the ducts, but apparently are carried along the plexuses of sympathetic fibers surrounding the smaller blood vessels outside the carotid sheath. The individual branches not accompanying any blood vessels would travel along the duct for distances up to several hundred microns, with occasional branches, to terminate without any specializations. The nerve fibers were encased in a Schwann cell sheath which in some cases only partially surrounded the fibers. Several of the axon profiles contained synaptic vesicles including small granular (or dense-cored) and agranular vesicles and a few large synaptic vesicles. In all cases observed, the axons and their Schwann cell sheath were located in the adventitia outside the smooth muscle cells.

Notes: Chick embryos were hypophysectomized by partial decapitation at 33 hours of incubation and the subsequent morphogenesis and growth of the whole embryo and the growth, histology and histochemistry of the tibia studied.Twenty-five percent of the increase in body weight which normally occurs between 12 and 18 days of incubation and 60% of the normal growth of the tibia over the same period failed to occur in the hypophysectomized embryos. Histological studies indicated that the diminished skeletal growth resulted from reduced proliferation of chondroblasts within the epiphyseal growth zone and from reduced deposition of acid mucopolysaccharides into the cartilaginous matrix. The differentiation and hypertrophy of the chondrocytes produced in the hypophysectomized embryos was not affected. Therefore, the pituitary gland exerts considerable control over the development of the cartilaginous skeleton in the embryonic chick.Osteogenesis was reduced as a consequence of the reduced chondrogenesis in the long bones from the hypophysectomized embryos.

Notes: The serosal surfaces of major organs and tissues of the body cavities have been examined by scanning electron microscopy following fixation and critical point drying. The micrographs show that these surfaces are covered with microvilli and that the population is most dense on tissues that move about most actively in the body cavities. Radiating from the sides of the microvilli are many fine strands (150 Å, average diameter) which interconnect with each other and adjacent microvilli. Transmission electron microscopic studies of material treated with thorium dioxide at low pH or stained with ruthenium red, reveal these strands to be (1) polyanionic in nature and (2) to arise from a surface glycocalyx which coats the microvilli and intervillar surfaces. It is proposed that the serosal microvilli, together with their glycocalyx, harbor a layer of serious exudate and thereby create a slippery cushion designed to protect the thin mesothelium from frictional damage.