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Notes: Muscles of the perineal region were dissected in 20 cats. Levator ani muscle was composed of two parts: iliocaudalis and puboischiocaudalis; both parts inserted entirely on caudal vertebrae, as did the coccygeus muscle. A well developed band of smooth muscle, the pars analis of retractor penis (clitoridis), inserted on the anal canal to retract the anus. The external anal sphincter had pars caudalis and pars cranialis divisions, the latter covered paired anal sacs. In addition, a distinct sphincter encircled each anal sac duct. In the male, levator scroti muscle originated from external anal sphincter. There was no continuity between external anal sphincter and bulbospongiosus muscles. Cremaster muscles were absent in the cat. In the female, pars cranialis of external anal sphincter gave origin to the constrictor vestibuli muscle, and pars caudalis to constrictor vulvae muscle. Bulboglandularis muscles were present in both sexes. Urethralis, ischiourethralis, and ischiocavernosus muscles in the cat were similar to other quadripeds.

Notes: Collapse of the left lung in adult mice is followed by an increased mitotic incidence (MI) in the right lung which persists for approximately four days after operation. This compensatory increase in MI does not occur if the left thoracic cavity is packed with an implant of cotton wool which prevents hyperinflation of the right lung. The rate of incorporation of labelled thymidine per unit of DNA (RIT) is higher in the right than in the left lung of unoperated animals but after collapse of the left lung there is a reduction in the ratio of right to left in respect of RIT. These differences in RIT do not appear to correspond to changes in the rate at which cells enter DNA synthesis and it is suggested that they are due to differences in vascularisation between the right and left lungs. The compensatory increase in MI which follows unilateral collapse is not due to loss of tissue mass, to tissue damage or to the direct effects of the increased physiological load placed upon the remaining functional tissue. It is suggested that hyperinflation of the right lung causes changes in the rate of blood flow through that part of the organ and that, in consequence, there is a change in the local concentration of metabolites including those whose function is to regulate the mitotic rate.

Notes: The granule-containing cells in the wall of the arch of the aorta proximal to its union with the ductus arteriosus in young chicks were examined by electron microscopy. These cells contain many electron-opaque vesicles, about 1500 Å in an average diameter, and show basically similar cytological characteristics to the granule-containing cells described in autonomic ganglia, around the abdominal aorta, and in the carotid body of mammals. Occasionally the cells are in close apposition to smooth muscle cells, fibroblasts or endothelial cells. Other surfaces of the granule-containing cells are partly covered by satellite cells. Synapses are rarely found on the granule-containing cells in the tunica media of the aorta.A few bundles of elongated cells which enclose several nerve fibers in the cytoplasm penetrate perpendicularly into the tunica media of the aorta. In these bundles are also a few granule-containing cells. Three types of nerve endings terminate on the granule-containing cells; that is, endings with small clear synaptic vesicles, with small cored vesicles, and with large cored vesicles. In addition, presumptive afferent nerve endings are found in the bundles. They show a variable diameter along their tortuous courses and contain numerous mitochondria.

Notes: Because of a major (Ag-B) histoincompatibility, organs transplanted from Lewis (LE) to Brown Norway (BN) rats are acutely rejected. This immunological rejection can be prevented by inoculating BN rats at birth with (BN × LE)F-1 hybrid cells. However, the source of these cells is important since only those derived from the bone marrow are effective in inducing tolerance of LE skin grafts whereas both marrow derived cells as well as those originating from the lymph nodes can induce tolerance of LE hearts. The present study was undertaken to compare the efficacy of cells derived from the bone marrow and the lymph nodes of (BN × LE)F-1 rats to induce unresponsiveness to LE neurons in BN recipients. In untreated rats, all neurons in sensory (vagal nodose) and sympathetic (superior cervical) ganglia transplanted from LE rats to the anterior chamber of the eye or implanted into the sternomastoid muscle of BN recipients were rejected within 35 days. However, when neonatal BN rats were inoculated with adult (BN × LE)F-1 hybrid bone marrow or lymph node cells and challenged as adults with LE ganglia grafts many neurons survived beyond 100 days. This result demonstrates that tolerance of Ag-B incompatible neurons can be achieved with either bone marrow or lymph node cells. Moreover, since tolerance can be produced in rats exhibiting major or minor histoincompatibilities, this method of immunosuppression offers one way of preventing neuronal rejection which occurs acutely in Ag-B incompatible and chronically in Ag-B compatible ganglia homografts.

Notes: Ultrastructural changes of rat blastocysts during delayed implantation were studied 16, 20, 24 or 30 hours after estrogen was given to induce implantation.In the inner cell mass the presence of long cytoplasmic processes penetrating deeply into the neighboring inner cell mass cells is seen at 16 hours. Most cells also show an increased number of ribosomes, polyribosomes and granular endoplasmic reticulum.The trophoblast is featured by the formation of large amounts of glycogen and many inclusion bodies. Glycogen granules appear first in some abembryonic trophoblast cells at 16 hours, and spread to the embryonic pole at 24 hours. New inclusion bodies appear sequentially: multivesicular bodies at 20 hours, multigranular bodies at 24 hours and lamellar bodies at 30 hours. The functions of these inclusion bodies remain to be studied.

Notes: Study of the developing chick retina with the electron microscope revealed that dyad ribbon synapses begin to form in the inner plexiform layer before synaptic ribbons begin to appear in photoreceptor terminals of the outer plexiform layer. This centrifugal (inner to outer) sequence of synaptogenesis in the predominantly cone retina of the chick differs from the centripetal sequence that has been reported for the predominantly rod retinas of the mouse and rat. This difference does not favor the hypothesis, suggested by others, that the photo-receptor may influence the maturation of inner retinal elements. The different patterns of synaptogenesis are discussed briefly with reference to anatomical differences between the retinas of different species.

Notes: The processes of myogenesis and elastogenesis are studied under the electron microscope in developing rat lungs, throughout the 15th to the 21st days of the gestation period. Myogenesis follows bronchial development and stops at the beginning of the alveolar zone, at the primitive respiratory bronchiole level. Elastogenesis appears at the periphery of the myoblasts during their differentiation. Thin myofilaments only are observed within myoblasts and their formation precedes that of dense bodies.Primitive respiratory bronchioles are visible on the 19th day and are characterized by an early elastogenesis carried out by fibroblasts. At this stage there are no elastic fibers around the alveolar tubules. Then (20th and 21st days) elastogenesis spreads throughout the alveolar zone, accompanying the alveolization process. Peculiar morphological characteristics of the pulmonary fibroblast are underlined. In relation to both muscular cells and fibroblasts the fine structural features of the rat pulmonary elastogenesis are identical to those previously described in other organs. Myoblasts and fibroblasts probably originate from the same primitive mesenchymal cell. Their differentiation depends on the zone where they are located. The relations between connective tissue and epithelial cell differentiation suggest a control of lung development by means of reciprocal induction processes.

Notes: The reproductive biology of Carollia was investigated histologically in 113 females sacrificed at timed intervals after mating in a laboratory colony. A high incidence (44%) of non-pregnant animals could be partially attributed to occasional mating activity at times other than close to ovulation. Breeding success also improved as the males and females were housed together for increasing periods of time. At least 25% of the bats had adrenal cortical-like tissue in the vicinity of the ovaries.Ovulation of the single ovum usually occurred within 48 hours of the onset of female receptivity to the male. Both ovaries were functional, but there was a tendency towards the alternation of successive ovulations. The blastocyst stage was reached and the zona pellucida was lost in the oviduct between days 10 and 12 post-coitum. Blastocysts entered the uterus between days 13 and 16. The slow tubal journey of the ovum is presumably related to the occurrence of mensturation close to the time of ovulation and to the fact that most uterine growth is deferred until after ovulation. Additional ovulations and a new conception were observed during the course of several preexisting pregnancies.Differential stimulation of the two oviducts was evident both prior to and after ovulation. The oviductal secretory cells became engorged during the tubal journey of the ovum with a substance that was Alcian blue 8GX- and Giemsa (pH 4.5)-negative. Occasionally this material could be stained by the PAS procedure.

Notes: The number and spatial relations of muscle spindles in the extensor indicis have been determined. Approximately forty spindles lie adjacent to the motor end plate zone dispersed rather equally through this area of the muscle with a modest increase in density among the distally originating fibers. A study of the entire innervation pattern of this muscle has also been completed.These findings have greatly facilitated the isolation of spindles for electron microscopic study and attempts to perform in vivo recording from the sensory nerves of muscle spindles in this laboratory. It is now possible, with the aid of suitable magnification and stimulating and recording devices, to more rapidly find muscle spindles relative to the gross innervation and the easily located motor end plate zone.

Notes: The ependymal tanycytes lining the ventral basal region of the third ventricle were studied in female rats during different stages of the estrous cycle. At mid-diestrus, the apical membranes of tanycytes were shown to be devoid of microvilli and of other surface irregularities. During proestrus, a multitude of microvilli and small bulbous protrusions characterize this region of the ventricular wall. These surface disruptions persist through estrus and disappear during diestrus. In addition, so-called supraependymal cells were observed and counted. Their numbers also vary with respect to the estrous cycle. The significance of these changes is discussed with respect to a possible mechanism for transporting substances from the cerebrospinal fluid (CSF) to the parenchyma of the hypothalamus and to the circulation.

Notes: Innervation to muscles of the feline perineum was examined by gross dissection of the sacral nerve plexus and quantitation of efferent and afferent myelinated fibers in selected nerves derived from the plexus. In addition, distribution of muscle fiber sizes and muscle spindle content were determined for muscles innervated by the nerves studied.Efferent myelinated fiber populations were bimodal in nerves innervating muscles with many spindles and unimodal in nerves innervating muscles in which few or no spindles were observed. Coccygeus and levator ani muscles had similar numbers of muscle spindles, but the spindles were different in the two muscles based on afferent innervation. In both coccygeous and external anal sphincter muscles, primary spindle endings must be associated with relatively small afferent nerve fibers. The pelvic urethra received more large myelinated afferent fibers than the penis. The three divisions of the external anal sphincter muscle had three distinct populations of muscle fibers, based on size distribution. The homologous bulbospongiosus and constrictor vulvae muscles had different populations of muscle fibers.

Notes: The fathead minnow, Pimephales promelas (Rafinesque), has been laboratory bred and the early embryos staged and described. At 23°C the embryo requires 33 hours to reach the 13-somite stage. This period of early embryonic development has been divided into 12 stages. The description of each of these stages is accompanied by photographs.

Notes: Each of the bilateral nasal glands of Dipsosaurus is surrounded by a thin cartilagenous capsule. A short excretory duct leads to the vestibule of the nasal cavity. This duct connects with the branched principal secretory tubules that end in small terminal segments. Tall columnar cells line the principal secretory tubules, but mucous and tuft cells form the terminal elements. In salt-stressed animals the spaces between dark and light principal secretory cells are dilated. Potassium-dependent, ouabain sensitive, adenosine triphosphatase (Ernst, '72a) was localized within the lateral plications of the principal secretory cells and in the apical microvilli of the tuft cells. These observations are consistent with current concepts of ion transport in salt-secreting epithelia, and they suggest that the tuft cells, not found in avian salt glands, play a role in the unusual physiology (Templeton, '66) of the nasal glands in this reptile.

Notes: Electron microscopic studies were made of hepatocytes from sham-operated rats, adrenalectomized animals fasted 15 hours, and adrenalectomized rats fasted 15 hours but given a single I.P. injection (10 mg) of cortisone acetate. The objective of this work was to define the earliest morphological response of hepatocytes to injection of a glucocorticoid and to provide additional information on the mechanism of hormone action at the cellular level. Hepatocytes from fasted, adrenalectomized rats contained no glycogen particles and very little smooth endoplasmic reticulum (SER). In addition the rough endoplasmic reticulum was disorganized and showed fewer ribosomes and polysomes than found in liver cells from sham-operated rats. Two hours after glucocorticoid injection glycogen particles were seen in numerous centrilobular cells and some periportal hepatocytes. Elements of SER were associated with the glycogen particles. By 4 hours after hormone injection abundant glycogen was found in all hepatocytes. Centrilobular cells showed dispersed glycogen with extensive tubules of SER associated with the glycogen particles. Periportal hepatocytes accumulated glycogen as dense masses scattered throughout the cytosome. SER occurred mainly at the edges of the glycogen masses. Midlobular cells showed glycogen patterns intermediate between periportal and centrilobular cells; masses of dispersed glycogen with abundant SER occurred within and around the glycogen areas of the cells. Glucocorticoid stimulation also caused cisternae of RER to align in parallel arrays, and more ribosomes and polysomes appeared on membranes of RER than in similar cells from adrenalectomized rats. The interpretation is offered that the glucocorticoid-stimulated proliferation of SER is the morphological expression of induced microsomal enzyme synthesis (glucose-6-phosphatase) known to occur under these hormonal conditions.

Notes: Minute amounts of white or brown adipose tissue can be localized in situ within seconds by covering the organ surfaces with an alkaline solution of dithizon (diphenylthiocarbazone) in alcohol and water. The adipose tissues stain deep green, while the other organs remain unstained, or appear in various shades of pink and red. This technique has been successfully applied to various groups of vertebrates (mammals, birds, reptiles, amphibians and fishes), and it works in fresh, in deep frozen and in formalin-fixed specimens. It fails after tissue fixation in mercuric chloride-containing fluids. In vitro studies show that the staining reaction is due to (1) a preferential solubility of small amounts of dithizon in adipose tissue lipids, and (2) the development of a green color, which appears when dithizon dissolves in lipids or organic solvents.

Notes: Factors contributing to the retino-tectal course of the optic nerves in cyclopic and synophthalmic zebrafish embryos were evaluated. The eye abnormalities were produced by immersing blastula stage eggs in 3% ethanol for two hours. Approximately 50% of cyclopic eyes produced one optic nerve that exits from the eye to innervate one optic tectum. The remaining half of the cyclopic embryos formed optic nerves that were unable to exit from the eyes.In the synophthalmic embryos, two optic nerves were always produced. These nerves either joined within the partially fused retinas, or shortly after exit from the eyes, to form one nerve which entered the brain and innervated only one optic tectum. Crossing over was not seen within the fused eyes or after exit from the eyes.The resultant single optic nerves in the cyclopic and synophthalmic embryos innervated the side of the brain penetrated by the nerve. They entered in the floor of the forebrain, diencephalon, or midbrain, usually asymmetrically. Axial growth, directional orientation, and contact guidance of matrix configurations appeared an adequate explanation for the establishment of the retino-tectal pathway.

Notes: The seminal vesicle secretes a variety of substances into semen, ranging from small molecules to enzymes. The formation of protein components of the seminal vesicle secretion was studied in male rats following an injection of leucine-3H. Samples of seminal vesicle were fixed and prepared for light and electron microscope radioautography at intervals ranging between four minutes and two hours after the injection. In specimens prepared four minutes after administration of the precursor, the majority of silver grains overlay the rough endoplasmic reticulum. At subsequent intervals, the proportion of grains over the endoplasmic reticulum declined, and peaks of labeling were observed sequentially over the Golgi apparatus and over secretory vacuoles. The maximal labeling of the Golgi apparatus was attained between 10 and 30 minutes after the injection. Secretory vacuoles acquired their greatest radioactivity 30 minutes following administration of the leucine-3H. Labeled secretions began to appear in the lumen 30 minutes after the injection, and they became heavily labeled by one hour. The results suggest that secretory proteins are synthesized in the rough endoplasmic reticulum and transported rapidly to the Golgi apparatus where secretory vacuoles are formed. The secretory vacuoles migrate to the apical ends of the cells and discharge their contents into the lumen. The transport and release of secretory proteins in the seminal vesicle is unusually rapid and exceeds the rate in many other protein secreting cells, including that of the ventral prostate.

Notes: Glycol dehydration followed by rehydration prior to conventional fixation appears to demonstrate the essential identity of the thick filaments observed in unfixed, glycol dehydrated and conventionally fixed smooth muscle. Observed differences in the solubilities of actin and myosin filaments also suggest that the thick filaments of smooth muscle are not formed by the apposition of actin filaments or by the deposition of myosin upon actin filaments. Evidence that the thick filaments of smooth muscle are not formed by an unnatural aggregation of smaller myosin aggregates or by the dissociation of myosin “ribbons” during tissue preparation is also reported. Examinations of smooth muscle contracted or relaxed by pharmacological agents appear to indicate that the myosin content of smooth muscle is aggregated into filaments in both the contracted and relaxed cell.

Notes: Ovarian and uterine morphological changes were examined in the maturing Holtzman rat, ages 22-40 days, using routine histological procedures. These findings were then correlated with serum follicle stimulating hormone (FSH) and luteinizing hormone (LH), in an effort to trace the sequence of events involved in the onset of puberty (i.e., the initiation of cyclicity) which occurred most consistently in our rats at 38 days of age. Ovaries exhibited no significant weight increases prior to day 36. However, microscopic changes became apparent as early as day 30, and continued to day 38, the day of the gonadotropin surge. During this time interval, the proportion of large type 6-7 (potentially estrogen secreting follicles) increased dramatically relative to non-antrum containing follicles. An increasingly hypertrophied and well differentiated theca interna of the larger follicles was also characteristic of this age interval. Closely paralleling the sequence of follicular maturation, quantitative and qualitative increases in all layers of the uterus occurred. As early as day 32, the luminal epithelium had increased some three to four-fold over earlier age groups. Similarly, the stromal endometrium and myometrium increased significantly at this time. Further increments occurred through day 34, with a leveling off at this time.Serum FSH showed no significant increases prior to day 38, at which time levels increased some two-fold over previously existing levels. In contrast, LH remained tonic until days 34 and 36, at which time subthreshold elevations occurred. On day 38, LH rose some 40-fold over pre-existing levels. Serum prolactin followed a similar pattern; levels became detectable at 33 days of age with marked elevations seen on day 35 and on day 38 of age.From quantitative and qualitative analysis of ovarian and uterine morphology with subsequent correlations to serum gonadotropins over the maturing process, we conclude that the ovary possibly acts as a “Zeitgeber” for the gonadotropin surge and ovulation.

Notes: The behavior of somatic cell chromatoid bodies in the planarian Dugesia dorotocephala during mitosis has been studied by electron microscopy. The relatively undifferentiated beta (progenitor) cells are the only somatic cells containing chromatoid bodies and also are the only dividing somatic cells. Somatic cell chromatoid bodies are known to disappear as differentiation takes place and reappear when dedifferentiation occurs. Interphase and prophase beta cells have juxtanuclear and peripheral cytoplasmic chromatoid bodies. There is no ultrastructural evidence to suggest they are derived from formed nuclear material. During metaphase and anaphase, the chromatoid bodies are segregated from the chromosomes and adjacent cytoplasm by cups of double membranes. By the completion of telophase, the chromatoid body size and number immediately adjacent to the nucleus is markedly decreased and extremely large chromatoid bodies may be found further out in the cytoplasm. These findings are compared to the behavior of germ cell chromatoid bodies and discussed in terms of their possible significance and function.

Notes: The soleus muscle is widely used in biochemical and physiological investigations as an example of a slow-twitch red muscle, and it has been assumed, for the most part, that it consists of a homogeneous population of either red or intermediate fibers. In the present study, the cytological composition of this muscle was examined in four commonly studied species, namely the rat, guinea pig, rabbit and cat. Using the form and distribution of mitochondria as the principal criteria for identification, two distinct types of muscle fibers can be recognized in the soleus of the guinea pig and rabbit as well as the rat. The soleus muscle is therefore not homogeneous in either species. Preliminary observations suggest that the soleus of the cat is likewise not homogeneous. In addition, although the fibers resemble red and intermediate fibers in other skeletal muscles, the resemblance is only superficial. In the two fiber types of the rat and guinea pig soleus, the Z line is characteristically wide, and therefore, based on this criterion, the fibers are not equivalent to either the red or intermediate fibers of other muscles.

Notes: Normally, the size of pancreatic acini is remarkably decreased after birth in the rat.Administration of water or milk on day 21 of gestation resulted in decreased acinar size a day later in intact fetuses and in fetuses decapitated immediately after administration of water or milk. The same treatments of premature newborn rats obtained by Caesarean section on day 22 of gestation induced similar effects a day later On the other hand, in starved Caesarean newborn rats, there were no histologic changes in acini. In spontaneous newborn rats which were allowed to suckle maternal milk and then starved for one day, there was an increase in acinar size as compared with that of 2-day-old normal rats.These results suggest that the fetal pancreatic acini at least near term (on day 21 of gestation) can respond to some signals conveyed from digestive tracts which have responded to exogenous stimuli, that the brain during fetal days does not play any role in digestive tract-pancreatic acini interrelations in secretion of zymogen granules and that the neonatal decrease in acinar size is caused by the intake of maternal milk.

Notes: Explants of six-day chick embryo skin, cultivated in a chemically defined medium (Waymouth Medium MB 752/1) for one to eight days were fixed and processed for electron microscopic study. Excellent development and differentiation of chick embryo skin was recorded. The skin cultivated in vitro matured much earlier than in ovo. After one day in vitro the morphology of the skin is similar in the stage of development to that of a 10-12 day embryo skin in ovo. After two or four days in culture, the skins are comparable to those of 12-14 day or 15-16 day in ovo embryos, respectively. The periderm of the epidermis was highly developed and contained a large number of peridermal granules after six days of culture. The skin proper, contained a granular layer, which resembled the skin of a 17-day embryo. Complete cornification of the epidermis was observed for the first time in vitro after 8 days of incubation. Keratohyalin granules which were claimed to be absent in avian skin, were observed.

Notes: Five different proteolytic enzymes, trypsin, pronase, collagenase, papain and ficin, were tested for their ability to liberate mononucleated myogenic cells from adult rat muscle. Fragments of leg and thigh muscle from 350-400 gm rats were incubated with enzyme for one hour and mononucleated cells were separated from the partially digested fragments by centrifugation. Myogenic capacity of the isolated cells was tested in culture using procedures known to support differentiation of embryonic rat muscle. Although all the enzymes released viable cells from the muscle, myogenesis in vitro was obtained only from cells liberated by trypsin or pronase. The other three enzymes released fibroblasts, macrophages and fat cells but no presumptive myoblasts. Light and electron microscopic examination of the digested muscle revealed that the enzymatic release of myogenic cells is dependent upon removal of the basement lamina surrounding the fibers. Trypsin and pronase dissolve the basement lamina, whereas collagenase, papain or ficin do not. These findings demonstrate that a population of myogenic stem cells exists in fully mature, non-regenerating adult muscle. The frequency of these cells and the conditions required for their release suggest that they are identical with the muscle satellite cells.

Notes: In order to investigate the postnatal growth of the gas exchange apparatus, the lungs of rats aged 1, 4, 7, 10, 13, and 21 days were fixed by intra-tracheal instillation of glutaraldehyde. The analysis and interpretation of the morphological changes observed by light and electron microscopy were based on the results of previous morphometric and autoradiographic studies performed on the same material.The newborn rat has no alveoli, but breathes with smooth walled air channels and saccules, which correspond to the prospective alveolar ducts and alveolar sacs, respectively. The bulk of alveoli are formed between days 4 and 13 by a rapid outgrowth of secondary septa from the primary septa present at birth. The arrangement of elastic fibers during this period suggests that these may play a role in septal outgrowth. Based on ultrastructural observations a model is described for the capillarisation of the secondary septa. Some evidence is given that alveoli may also be formed by outpouchings in the walls of terminal bronchioles.Primary and secondary septa have initially an immature appearance. They both show an apparently double capillary network, whereas the mature interalveolar septum is just wide enough to accommodate a single capillary. Possible mechanisms for this structural transformation which occurs within three weeks after birth are discussed.

Notes: Combined morphometric and autoradiographic methods were used to analyze the postnatal growth of rat lung from 1-21 days after birth. Each cell population had distinct growth patterns with an increase in the number of fibroblasts and capillary endothelial cells largely determining the increase in interstitial volume and capillary surface, respectively. The height of proliferation activity in mesodermally-derived cells was concurrent with the outgrowth of secondary alveolar septa (between days 4 and 13). Analysis of the location of labeled cells on day 7 showed that the higher labeling index on septal crests could be ascribed to the proliferative activity of fibroblasts and endothelial cells.Within the alveolar epithelium only the type II alveolar cells had a detectable labeling index. Over the first week, the number of type I epithelial cells steadily increased while the number of type II cells remained constant. Subsequently the number of type II cells increased rapidly, reached a peak on day 13 and then decreased, whereas type I cells continued to increase in number. These facts led us to consider that type II epithelial cells may represent the stem cell population of alveolar epithelium. The height of proliferative activity of type II cells on day 7 coincided with the outgrowth of septal crests and was followed by the steepest increase in number of type I and II cells.Between the 10th and 21st day labeling indices rapidly declined, cell production became undetectable after day 13. Increase in alveolar and capillary surface area however continued, resulting in a thinning of the interstitial layer and of the epithelial and endothelial sheets.

Notes: The surface topography of palatal shelves was examined by scanning electron microscopy prior to and during secondary palate formation in 72 therapeutically aborted human embryos and fetuses ranging in age from 37 days to 12 weeks (post-fertilization). Alterations in epithelial surface appearance were observed in the prospective region of fusion prior to contact between the shelves. First seen as an elliptical area along the anterior portion of the presumptive medial edge, a zone of alteration spread progressively along the anterior four-fifths of the medial edge prior to shelf contact, and continued along the posterior one-fifth of the shelf as fusion proceeded. The altered zone eventually extended onto the oral surface in the middle of the shelf but was restricted to a narrow zone along the medial edge posteriorly. Initially characterized by elongation and “intertwining” of superficial cells, alterations later included cell death, desquamation and possible active migration of surface cells. The shelf epithelium subjacent to the zone of alteration exhibited increased irregularity in thickness and numerous “invaginations” into the underlying mesenchyme. These alterations are thought to reflect intrinsic changes within the shelf and may play a role in the fusion process. Evidence for surface remodeling following fusion was also observed.

Notes: Mouse blastocysts were grown in vitro and the ultrastructure of resulting egg cylinders was compared with the ultrastructure of egg cylinders isolated from uterus. Egg cylinders grown in vitro had two or three germ layers and were attached to the bottom of the dish through the layer of trophoblastic cells. The entoderm was composed of two cell types intermixed haphazardly: (1) One type had numerous microvilli on the free surface and a large number of dense bodies, autophagic vacuoles, big and small vacuoles and myelin figures in the cytoplasm. (2) The other type had rich, rough endoplasmic reticulum with wide cisternae. The cisternae were filled with fine, granular material similar to that found as a thick membrane separating the entodermal layer from the rest of the embryo. The first type of cell was ultrastructurally similar to cells of the visceral entoderm of egg cylinders isolated from uterus and the second type was similar to cells of the parietal entoderm. The thick basement membrane observed in embryos grown in vitro was similar to Reichert's membrane. Parietal entoderm and Reichert's membrane were never found as separate structures in embryos grown in vitro. It is probable that the entodermal cells in blastocysts differentiate in vitro into both parietal and visceral entodermal cells within the same layer. Mesodermal and ectodermal cells of vitral embryos were similar to such cells in the egg cylinders isolated from the uterus. The cytoplasm was filled with free ribosomes in the form of polysomes and also contained a few profiles of endoplasmic reticulum, well developed mitochondria and Golgi apparatus. Intercellular spaces between mesodermal cells were large and the cells were not attached to one another. Ectodermal cells were tightly packed and inter-connected with numerous desmosomes. The ultrastructure of egg cylinders in vitro and in vivo was similar. Observed differences might be caused by culture conditions and some of them probably represented the changing pattern of differentiation in vitro.

Notes: The phyllostomid bat, Macrotus waterhousii, undergoes delayed development. Implantation occurs early in the nine-month gestation, but the blastocyst remains relatively dormant until the sixth month when a chorioallantoic, hemodichorial placenta forms and a two and one-half to three-month growth pattern occurs leading to parturition.The barrier in the chorioallantoic placenta at first includes maternal capillary endothelium, but during the early part of the rapid growth phase the endothelium is replaced by blocks of syncytial trophoblast which penetrate the basal lamina. The basal lamina then apparently thickens and remains as the intrasyncytial lamina. Thus, the definitive barrier for maternal nutrients consists in order of passage of syncytial blocks, intrasyncytial lamina, syncytiotrophoblast, cytotrophoblast, fetal basal lamina and capillary endothelium.

Notes: The satellite cell population in mouse lumbrical muscle is quantitated at ages 7, 14, 21 and 30 days. Satellite cell nuclei comprise nearly 30% of the nuclei within the fiber basal lamina in the youngest animals studied. Growth is accompanied by a rapid decrease in the percentage of satellite cell nuclei. This is not accounted for by the increase in myonuclei, but rather there is an absolute decrease in the number of satellite cells. This loss in satellite cells occurs in spite of their high rate of division and is explained by a high percentage incorporation of the daughter cells of satellite divisions. It is further suggested that the percent incorporation of available cells decreases with age.

Notes: The minimum period of uterine exposure required by ejaculated boar spermatozoa as a preliminary to rapid capacitation has been determined after natural or surgical deposition of sperm samples directly into the uterine lumen. Twenty-four oestrous gilts were mated or inseminated close to the time of ovulation, and 15, 30, 45 or 60 minutes later, the Fallopian tubes were separated from the uterine cornua. The tubes were flushed at pre-arranged intervals during a second intervention, and the proportion of eggs penetrated and activated examined by phase-contrast microscopy.On the basis of 166 eggs recovered from eighteen mated gilts, a period of uterine exposure as brief as 30 minutes, when followed by a tubal residence of approximately three hours, permitted 30.3% of the eggs to be activated; this proportion increased to 51.6% and 60.5% if the tubes were isolated 45 or 60 minutes, respectively, after mating (p 〈 0.001), as did the mean number of spermatozoa associated with the eggs. When the cornua were separated from the tubes 15 minutes after semen deposition into the uterus of six animals, 11.3% of 62 eggs were fertilized during the ensuing three and one half hours, but very few spermatozoa had reached and/or attached to the eggs in this group.It is concluded that a population of boar spermatozoa potentially capable of effecting fertilization may enter the tubes within 15 to 30 minutes of mating near the time of ovulation, and that such vanguard spermatozoa can activate a proportion of the eggs within a further two to three hours. Thus, from a temporal point of view, the major components of the capacitation process in oestrous pigs are inferred to take place in the Fallopian tubes.

Notes: The localization of alkaline phosphatase activity in the ultimobranchial bodies was studied at the fine structural level in Holtzman rat embryos from the 15th to the 19th day of gestation, and also in four-week old rats of the same strain. In the embryos, no alkaline phosphatase activity was found before the 17th day of gestation. From that day on, plasma membranes of glycogen-rich cells show the reaction product regardless of their location in the wall of the ultimobranchial bodies. However, when the same cells are seen on cell cords of the median thyroid, they are negative. In the four-week old rats, plasma membranes of ultimobranchial cells are strongly reactive. C cells are negative both before and after birth. Small thyroid follicular lumina with positive apical cell membranes are also noted in four-week old rats. These positive thyroid follicles are not more differentiated than those previously described in 19-day old rat embryos. It is concluded that new thyroid follicles are formed after birth. These results are discussed in relation to the hypothesis that when ultimobranchial cells are transformed into follicular cells, they undergo the same alkaline phosphatase changes as those observed during the maturation of follicular cells derived from the median thyroid primordium. The cytochemical method used is also criticized.

Notes: The patterns of the superficial veins of the cubital region were studied in 536 Indian subjects both living and dead. Three basic pattern types were noted. Type I had a median cubital vein joining the cephalic and basilic veins in the cubital region. Type II had the cephalic vein itself draining into the basilic vein in the cubital region. Type III showed the absence of a direct communication between the cephalic and basilic veins in the cubital region. The median vein of the forearm in these latter cases joined either of the cephalic and the basilic veins (type III A) or after bifurcating into a median cephalic and a median basilic vein joined both these veins (type III B). Type I was found to be the most common pattern (67.5%) followed by type II (19.5%), with types III A and III B accounting for 6% and 6.5% of the cases, respectively. Renaming of the median cubital vein as the oblique cubital vein because of its direction and renaming of the median basilic and lateral basilic veins as medial and lateral cubital veins since they follow the medial and lateral borders of cubital fossa respectively has been suggested.

Notes: The intramural arteries, arterioles and capillaries of the hearts of 23 crossbred pigs, six months old, of Yorkshire and Swedish landrace were presented.The vascular pattern was basically the same in both the ventricular walls. Large branches of two types emerged from the extramural arteries and traversed the myocardial wall, terminating in the subendocardial zone. The largest vessels supplied the papillary muscles and trabeculae carneae. The terminals of these branches formed the subendocardial anastomotic network. No other anastomoses were observed in the ventricular walls. The capillaries had a course parallel to the muscle fibers and anastomosed freely. Most of the interventricular septum was supplied by branches from both the left and the right descending arteries. Only a minor part of the septum was supplied by the anterior and posterior septal arteries.The ventricular vascular pattern of the pig was found to be very similar to that of the human heart. It was concluded that the pig, in contrast to the dog, has ideal attributes for comparative cardiovascular research in man.

Notes: The sequence of cytological events from sperm penetration of the oocyte until emergence of the blastocyst from the zona pellucida was studied in 1441 eggs from 134 animals in which the time of ovulation had been controlled precisely by gonadotrophin injection. Observations were also made on the rate of egg passage through the Fallopian tubes, on the process of denudation, and on the increase in numbers of spermatozoa associated with the zona pellucida.Eggs may be penetrated and activated within three hours of mating or insemination close to the time of induced ovulation. A decondensation and swelling of the chromatin is seen very soon after incorporation of the sperm head into the vitellus, and central apposition of the pronuclei occurs three to five hours later. The male pronucleus is slightly larger than the female, and a portion of the flagellum is frequently closely associated with it until late syngamy. Cleaved embryos can be recovered within 14 to 16 hours of sperm penetration, but the two-celled stage lasts only six to eight hours compared with 20 to 24 hours for the four-celled stage. Embryos enter the uterus at the latter stage approximately 46 hours after ovulation. Morulae of 16 to 32 cells can occasionally be observed late on the third day of development, and blastocysts are present on the fifth day. However, the zona pellucida is not shed until the sixth day, after which the trophoblast commences the massive elongation characteristic of this ungulate blastocyst.

Notes: Banded spindle-shaped structures consisting of packed cylindrical units were observed among the typical collagen fibrils in the notochord sheath or in the intercellular space between notochord cells of Salmo irideus larvae. The banded spindle-shaped structures showed a regular periodicity ranging from 750-1000 Å and cylindrical structures which appear to be packed in hexagonal arrays so that six cylinders surrounded a central cylinder. Both banded and cylindrical structures appeared to be the same bodies in three dimensions. These banded structures may originate from surrounding collagen fibrils.On the other hand, comb-shaped structures were found between the elastica externa and the collagen fibrils of the notochord sheath in newly hatched S. irideus larvae and in fry. The width of the structures was about 0.25 Å in the widest part. The banding showed a regular periodicity ranging from 500-600 Å. These structures may play a role in adhesion of the elastica externa to the underlying collagen fibrils of the notochord sheath.

Notes: The ruthenium red staining technique of Luft ('71b) was utilized in an electron microscopic investigation of developing and adult rat lung. Electron-dense deposits of ruthenium red-positive material were observed on all exposed surfaces of the tissue block, regardless of the stage of development. In the more central areas of the block, sites of ruthenium red binding changed with age. In early prenatal lung (days 16 to 20) dense accumulations of ruthenium red-positive material were found in association with the basement membranes of endodermal epithelial cells. Ruthenium red binding was also observed between adjacent epithelial cells; however, their luminal surfaces were negative. The main intracellular site of ruthenium red binding in intact cells was the lamellar body of the developing type II pulmonary epithelial cells. By day 21 of development, accumulations of granular product were observed in association with most lamellar bodies, as well as on epithelial cell luminal surfaces. Ruthenium red binding in postnatal tissue decreases with increasing age. By the second postnatal week, the predominant site of binding is the luminal surface of the type I and type II pulmonary epithelial cells. When compared to fetal and early neonatal stages, adult rat lung has a still more limited distribution of ruthenium red-positive material. Changes in the distribution of ruthenium red-positive material correlate with numerous morphologic and biochemical events in rat lung development.

Notes: Macroscopic and microscopic examination of adipose tissue was carried out in a series of 20 human fetuses, ranging in weight from 380-3032 gm, in an attempt to identify all areas of brown (multilocular) fat development and growth. Brown fat distribution in the human fetus takes the form of a highcollared vest affording coverage to the cervical, thoracic and abdominal viscera. Much of this fat lies deep within the body immediately outside the pleural and peritoneal membranes. the remainder overlies or borders muscles of the shoulder girdle and neck as distinct brown fat deposits deep to the subcutaneous layer of white (unilocular) fat. All brown fat bodies contain unilocular cells but they occur in very small numbers in the brown fat bodies of the posterior cervical triangle, anterior mediastinum and perirenal and suprailiac regions. Brown fat bodies usually develop along the course of large blood vessels and several of them develop direct vascular connections with the liver and kidneys. The total weight of fetal brown fat increases at a rate directly proportional to that of the liver and kidneys up to 2134 gm body weight and to that of the liver beyond this weight.

Notes: Projection from medial occipital cortex (area OB) to the nucleus of Darkschewitsch is demonstrated in six Macaca mulatta hemispheres by the technique of Fink and Heimer. Degeneration was present as well in the lateral pons, nucleus lateralis dorsalis, nucleus lateralis posterior, lateral pulvinar and nucleus parafascicularis. Centrum medianum, dorsal lateral geniculate body and interstitial nucleus of Cajal were spared.

Notes: Germ cells of the rat have been studied at the fine structural level from the time they are present in the epithelium of the embryonic gut until near the time of production of mature gametes in the adult. Particular attention has been paid to the form and location of dense, fibrous material (nuage) in the germ cells during that period of the life cycle. The nuage either exists as small discrete bodies in the cytoplasm or as “cementing material” situated in the interstices of mitochondrial clusters. It is present in primordial germ cells in the gut epithelium, in germ cells in indifferent gonads and in germ cells in sexually differentiated fetal, neonatal and adult rat gonads. It is sometimes associated with nuclear pores. Because it is present throughout much of the life cycle of the germ cells of male and female rats and it has been observed in various other mammals by previous workers, it is suggested here that it is a characteristic morphological feature of mammalian germ cells. In addition, there is considerable similarity in form and distribution of the nuage to the “polar granules” in insects and the “germinal plasm” in amphibians which are suggested to play a role in the determination of germ cells in these animals. The possibility that nuage may play a comparable role in mammals is considered.

Notes: The weight, density and percentage ash weight of the dry, fat-free osseous human skeleton have been examined from 16 weeks of gestation to 100 years of age. Data were drawn from 426 skeletons of American Whites and Negroes of both sexes.Weight increases exponentially in the fetus and continues to increase to early adulthood, most rapidly in the second decade. A decrease appears about the fourth decade and continues gradually. Estimated loss in skeletal weight throughout the adult period is, on the average, 15.6 gm per year. Proportionate contributions of divisions of the skeleton to its total weight change with age.Densities of bones follow the changing weight pattern. Volume and weight increase concomitantly to adulthood, when weight decreases but not volume.Percentage ash weight increases slightly in the total skeleton and in some bones during the fetal period, with no significant trend thereafter, indicating that change in weight of a dry, fat-free bone is accompanied by change in ash weight.Race and sex differences are not evident in the fetal skeleton, but become marked by the second decade of life: Negro skeletons exceed White skeletons and male skeletons exceed female skeletons in mean weight and density and, to a lesser degree, in percentage ash weight.

Notes: The objective was to study the fate of specific secretory cell types of the rat hypophysis when grown in primary monolayer cultures for periods ranging up to 32 days. The cells were identified immunohistochemically using peroxidase-labeled antibody. Early in the culture period TSH-cells were scarce and by 12 days they could no longer be identified. In most cultures LH-cells were well stained and common for eight to 12 days, after which they underwent involution. Growth hormone cells were a prominent feature up to six days but by 12 days they were declining in number, size, and stainability; in contrast, prolactin cells proliferated and were large and intensely stained throughout the period of study, ultimately becoming the dominant secretory cell type. Corticotropic cells also continued throughout the period of study without regression. Thus drastic shifts occur with time in the relative proportions of cell types in monolayer cultures of rat pituitary cells.

Notes: Distribution of mitotic nuclei in the biceps brachii of five day old mice has been studied after subcutaneous injection of 1 μCi/gm body weight 3H-thymidine. Serial transverse sections at 5 μm thickness were cut and the number of labeled nuclei per hundred fibers were determined on every fortieth section starting from the proximal end of the muscle.The proximal region of the muscle has significantly more labeled nuclei than either the belly region (P 〈 0.005) or the distal region (P 〈 0.001) of the muscle. The distal region of the muscle and the belly of the muscle did not differ significantly.Thus, most of the fiber elongation seems to take place at the proximal region of the muscle. As far as the transverse growth is concerned it appears that either every fiber at this stage is increasing in diameter or else the fibers which are undergoing an increase in diameter are randomly distributed throughout the body of the muscle, as no significant differences have been found in the percentage labeled nuclei in the four transverse areas of the muscle in the belly region.

Notes: The ultrastructure of articular cartilage of the femoral head was examined in growing male mice of strain C57Bl fed diets containing supplements of 25 or 40% corn oil for periods of 10 days, 2 and 4 weeks and 2 and 3 months. The ration containing 25% corn oil did not produce conspicuous effects. The ration containing 40% corn oil exerted a slight stimulation on the size, the ER, and the mitochondria of the articular chondrocytes. The findings are consistent with the long range effects of oil-enriched diets on the knee joints of mice and in particular with the failure of such diets to promote the development of osteoarthrosis in mice of strain C57Bl. The results are discussed in relation to earlier observations of the injurious action of diets containing comparable amounts of saturated fat.

Notes: The postnatal development of the ovary in the bank vole and vole was investigated in order to determine whether the earlier onset of puberty in the vole coincides with a difference in the speed of gonadal development during the immature period in the two species.The ovarian development differed in three respects: in the vole 4-10% of the germ cells are still oogonia when the animal is born, while in the bank vole oocytogenesis is completed during the embryonic period. Follicles develop earlier and more rapidly in the vole than in the bank vole. The early appearance of fluid accumulation in the follicles and the formation of “fluid sacs” in the vole ovary is characteristic.

Notes: The fine structural appearance of eight spontaneously polyspermic rabbit zygotes was studied. The zygotes were considered polyspermic only after they met all criteria that excluded other possibilities of the trinucleate state. The presence of accessory male pronuclei, with varying degrees of disintegration of their chromatin in zygotes of similar age, suggests that refertilization can occur during an interval of several hours after penetration of the primary sperm. All of the polyspermic zygotes contained cortical granules intermittently beneath the vitelline (plasma) membrane. One zygote possessed cortical granule-like structures with ill-defined or no limiting membrane. Formation of enveloping membranes around the incorporated accessory sperm head was precocious since it occurred prior to disintegration of the chromatin. Advanced stages of accessory pronuclei morphologically resembled the primary pronuclei in the same zygote. In seven out of eight zygotes the accessory male pronucleus was separated from the apposing male and female pronuclei. It was concluded that although the fully expanded accessory male pronucleus is similar to the pronuclei of monospermic fertilization, the temporal events of nuclear envelope formation were disturbed.

Notes: The numbers and diameters of nerve fibers were determined for the first time for all interganglionic rami of the sympathetic chain of the frog. The number of myelinated fibers ranged from 57 to 263 and was generally highest in the anterior portion (207) and lowest at the posterior end (57) of the chain. The exception was between the fourth and fifth ganglia where the middle splanchnic nerves arise  -  the number of myelinated fibers was highest here (263). Unmyelinated fiber counts were similar throughout the chain (417-814) except above and below the first sympathetic ganglion (7325 and 3026, respectively), and at the level where the middle splanchnic nerves arise (3780). Unmyelinated fibers constituted 75-97% of the fibers of the chain. The myelinated fibers ranged in diameter from 0.5 to 9.0 μ, 75% of them measuring between 1.5 and 3.0 μ. The diameter range for unmyelinated fibers was 0.1 to 5.0 μ with 78% being 0.1 to 1.0 μ.

Notes: Longitudinal sections through the incisors of the rat show a continuous layer of ameloblasts on the labial surface of the tooth. This layer contains the entire sequence of developmental stages in enamel production. Using 1 μm Epon sections from the upper and lower incisors of 100 gm male rats, the ameloblast layer was divided into three main zones which were themselves subdivided into regions: (1) Presecretory zone which includes (a) region of ameloblasts facing pulp, itself comprising a posterior portion (upper 172 ± 35 μm; lower 187 ± 37 μm) and an anterior portion (upper 458 ± 28 μm; lower 503 ± 36 μm); (b) region of ameloblasts facing dentin (upper 1210 ± 81 μm; lower 1381 ± 90 μm). (2) Secretory zone, (a) region of inner enamel secretion (upper 2573 ± 141 μm; lower 4274 ± 160 μm); (b) region of outer enamel secretion (upper 1211 ± 60 μm; lower 868 ± 72 μm). (3) Maturation zone (upper 7335 μm; lower 10615 μm), (a) region of postsecretory transition; (b) region of maturation proper, consisting of portions of ameloblasts with striated border and portions of ameloblasts with unmodified apices; (c) region of pigmentation; (d) region of reduced ameloblasts.These regions are readily identified using clear cut morphological criteria. Length measurements made on a group of 40 rats established the reproducibility of this classification. Therefore, this classification will be used as a basis for future studies of cell population kinetics.

Notes: The follicular cells of thyroid glands of intact rats respond to TSH challenge by an intense mitotic stimulation and a higher functional activity as measured by the epithelium height. In hypophysectomized rats the same intense response was observed when the thyroid was challenged immediately after hypophysectomy. However, one week later the mitotic response was almost completely absent and the functional response much weaker. This indicates that, although TSH is the main regulating factor of the functional activity and cell proliferation of the thyroid follicle, its effect is conditioned by additional factors. These factors may originate both from the anterior and/or posterior pituitary, since a significantly higher response was obtained by injecting anterior or posterior pituitary powder during the interval between hypophysectomy and TSH challenge. Prolactin, vasopressin and oxytocin also boosted the mitotic response to TSH. Posterior pituitary powder alone (without TSH challenge) was not mitogenic for the thyroid gland either in intact or hypophysectomized rats, while it was mitogenic for the adrenal glomerulosa. The low thyroid mitotic responsiveness does not reflect a general unspecific effect on mitoses of all cells, since the esophageal epithelium was not similarly affected by hypophysectomy or by replacement therapy.

Notes: The parietal layer of Bowman's capsule in man and rat has been examined by transmission and scanning electron microscopy. In both species, cilia were found to be present in a regular pattern occurring one per cell. The cilia differed in length between the immature and mature human kidney, but were consistently located near the edge of the cell nucleus. Since they are not numerous enough to have a significant propulsive role, we have postulated that they may have some other specific function. In addition to the cilia, microvilli were regularly observed on the surface of the parietal cells. They tended to be more numerous along the margins of the epithelial cells and, in contrast to the cilia, their pattern was highly variable. This variability probably indicates that they are transitory structures which can be increased or decreased in response to as yet unknown stimuli.

Notes: Previously reported methods for the electron microscopic visualization of the surface layer (surfactant) of the alveolar lining cells have proved less than ideal and further development in this area is needed. Two percent agar in glutaraldehyde injected into the respiratory tree concurrently with vascular perfusion seems to offer some real advantage over techniques described by others. The combination of glutaraldehyde and agar acts both as an obstruction that holds surfactant against the alveolar surface and as a fixative due to the buffered glutaraldehyde component. This technique offers more consistent results and more extensive demonstration of the surfactant layer over the alveolar surface.

Notes: A radioimmunoassay for insulin, together with ultrastructural observations of the endocrine pancreas, were utilized to investigate developmental aspects of insulin storage and secretion in the chick embryo. Immunoreactive insulin was detected from the fifth embryonic day onwards, in both the pancreas and blood plasma. In addition, margination of well-developed beta granules, and emiocytotic events were observed as early as the fifth embryonic day. The initial appearance of insulin, together with its subsequent developmental profile, correlate well with major metabolic events occurring in the embryonic chick, and are discussed in relation to a functionally responding system, the developing liver. The present data show that the chick endocrine pancreas has the potential for activity very early in development, and that insulin may be secreted at earlier embryonic stages than hitherto accepted.

Notes: Seminiferous tubules from mouse testes were studied with the light microscope after the efferent ductules had been ligated for 48 hours. As a consequence of ligation, the tubules became markedly distended by the fluid which they accumulated; the epithelium was reduced in height, and exhibited a significantly less complex stratification than in the normal. Longitudinal sections of the distended tubules, particularly those in the early stages of the seminiferous cycle, revealed pillar-like epithelial profiles arranged in a repetitive series. Each “pillar” consisted of Sertoli cell cytoplasm along with two generations of spermatids, the older generation embedded within the Sertoli cell, and the younger generation aligned, one cell above the other, along its sides. Oblique or grazing sections through tubules exhibiting the same stages of spermiogenesis revealed band-like epithelial profiles arranged in parallel array. The two types of epithelial configurations are interpreted as representing a series of circumferentially oriented ridges within the tubule. It is postulated that each spermatid generation within a ridge constitutes a single clone, and that it is the cytoplasmic bridges joining the spermatids, in combination with their attachment to the Sertoli cells, which provide the organization, delineation, and structural stability of the ridges.

Notes: A staining technique, in which basic fuchsin, methylene blue, and Azure II is applied to 0.5 μ sections of striated rat muscle embedded in epoxy resin, has given sufficient differentiation of five nuclear types found in the muscle fascicle to warrant its use as a valid method for identifying satellite cells with the light microscope. The validity of this technique was assessed by studying serial thin and thick sections of denervated rat hind limb muscles. Nuclei “typed” light microscopically were examined under the electron microscope to determine the type of cell in which they were located. This stain technique was then applied to determine the effect of denervation on the satellite cell population of the tibialis anterior and extensor digitorum longus. In control muscle of 200 gm rats, satellite cells represented 2% of the total nuclear population. Two and three weeks after denervation they accounted for 6% and 12%, respectively. In 800 gm rats, satellite cells accounted for 0.7% of the total nuclei found in the normal muscle. Denervation increased the percentage to 3% (at 2 weeks) and 5% (at 3 weeks). Paired satellite cells were infrequently observed; however, in 0.5 μ sections a significant number of satellite cells were found to be less than 0.7 μ from a myonucleus of the same fiber. A model is proposed to explain the increase in satellite cells following denervation.

Notes: Ultrasound studies of dorsalis pedis artery in 400 feet showed the artery to be absent in 2.25%, i.e., much less frequently than it was commonly claimed. Clearer understanding of this variation and its frequency may facilitate the diagnosis of peripheral circulatory disease.

Notes: Chronic hyperthyroidism was induced in radiothyroidectomized adult albino rats by feeding a diet of 0.3-0.4% desiccated thyroid for four to ten weeks. The left ventricle from control and hyperthyroid animals was examined with the electron microscope after perfusion fixation with 3% phosphate buffered glutaraldehyde and postfixation in 1% osmium tetroxide. No differences were discerned in the appearance of the Golgi zone, glycogen, lipid, lysosomes, sarcoplasmic reticulum, or the sarcomere ultrastructure of the ventricle from hyperthyroid animals compared with untreated animals. Changes were noted in the mitochondria. These included marked hypertrophy without increase in numbers and localized areas of vacuolization and disorientation of the cristae. Apparently these changes are reversible since the ventricular mitochondria of previously hyperthyroid animals allowed to return to a euthyroid state were indistinguishable from those seen in the control group.

Notes: Leydig cells appear in the hamster testis between 12 and 13 days gestation. The cells are round to oval, with prominent lipid droplets, abundant smooth endoplasmic reticulum, large mitochondria with tubular cristae and well developed Golgi complexes. Cells of this type are found in pairs and groups around interstitial blood vessels during the last three days of gestation and up to the fourth day after birth, when regressive changes begin to appear. During the second postnatal week, most cells in the interstitial regions are undifferentiated, with only a few scattered partially differentiated Leydig cells remaining. The time during which fully differentiated Leydig cells are present encompasses the period of sexual differentiation of the reproductive ducts and the critical period for differentiation of sexual behavior.

Notes: The forebrain of the isolated central nervous system of frogs was fixed by freeze substitution and studied with the electron microscope. The extracellular space (ECS) of brains kept for 15-20 min in a physiological salt solution at room temperature varied from an appreciable to a negligible one. In electron micrographs exhibiting a large ECS the tissue elements had a uniform electron density. The EMs with little space featured in some instances a moderate swelling of presynaptic terminals and other tissue elements. Brains kept in a cooled medium or a salt solution with MgCl2 added exhibited invariably an abundant ECS. Treating the brain with a 100 mM KCl solution 5-90 sec before freezing yielded EMs with a contracted ECS and swollen tissue elements, many of which could be identified as dendritic spines. This effect of KCl was in many experiments prevented by bathing the brain in a salt solution containing 10 mM MgCl2 or in a Ca-free solution.

Notes: The postnatal growth of the lung was quantitatively investigated in rats aged 1, 4, 7, 10, 13, 21, 44 and 131 days by light and electron microscopic morphometry.Lung volume (VL) increased first directly with body weight (W). After day 10 VL followed the function W0.70. Based on the quantitative findings the postnatal lung growth could be divided into three phases.1Lung expansion (up to day 4): Lung volume increase resulted almost exclusively from an 87% enlargement of the existing air spaces.2Tissue proliferation (day 4 to 13): All tissue compartments showed a pronounced mass increase, followed by a high gain in capillary volume. Alveolar and capillary surface areas (Sa, Sc) developed rapidly due to subdivision of the primitive air sacs.3Equilibrated growth (third week to adult age): An initial period of redistribution of tissue mass with septal lengthening and further rapid increase in Sa and Sc was followed by proportionate alveolar growth. In the adult further lengthening of the interalveolar septa or continued alveolar formation could not be excluded.During the period of fundamental internal remodelling of the lung, its function, as determined by the morphometric pulmonary diffusing capacity, was not impaired.

Notes: Fertile hens eggs were incubated 48 hours. Embryos were removed from the shell and the cervical region from each excised and placed in a balanced salt solution containing 1% trypsin for 40 minutes. Notochords were isolated by microdissection and further incubated in vitro 48 or 72 hours. Following trypsinization, unincubated notochords were rod-shaped and were shown by electron microscopy to be devoid of extracellular materials or contaminating mesenchymal cells. Extracellular materials, ultrastructurally indistinguishable from those in the perinotochordal connective tissue space in vivo, are present on the surfaces of cell clusters at 48 hours of in vitro incubation. Areas of fibrillogenesis, in which microfibrils are separated from the surface of cells by intermittent basement lamina, are common. At 72 hours of in vitro incubation fibrogenic activity is less evident, but occasionally intense concentrations of small and large microfibrils, basement lamina and other extracellular substances are seen adjacent to notochordal cell surfaces. These observations are of special interest in light of the known role of the notochord in embryonic induction and recent demonstrations that surface-associated substances (specifically collagen) are necessary for normal cytodifferentiation.

Notes: The effect of continuous darkness on diurnal variation of glycogen content in pineal cells of adult mice was investigated by means of a semiquantitative histochemical method. In dark-maintained mice, a diurnal rhythm in pineal glycogen content persisted for the first 7 days of darkness. After 14 days or longer of continuous darkness, however, a clear relationship between the glycogen content and time of day became less apparent. Reversed conditions of environmental lighting caused a complete reversal of the glycogen rhythm in the pineal as early as the fifth day. When mice that had been kept in reversed conditions of lighting for 7 days were exposed to continuous darkness, the reversed glycogen rhythm also persisted in darkness of 7 and 14 days, but it was abolished by darkness of 28 days. The nuclear density of pineal cells was significantly lower at 9 am than at 9 pm in controls. In dark-maintained mice, however, no significant diurnal variation in pineal cell size was generally evident except 2 and 3 days after the initiation of darkness.

Notes: Human muscle spindles are isolated from muscle biopsies of Extensor Indicis. A spindle rich portion of muscle is removed, placed into a modified Kreb's solution and microdissected for spindles. Intramuscular nerves and blood vessels provide helpful locating guides. Spindles can be dissected free of extrafusal muscle with an adequate length of nerve for in vitro recording. Another portion of muscle is stretched and placed into a 5% glutaraldehyde fixative in 0.1 M cacodylate buffer. Spindles are dissected free, postfixed, dehydrated, stained, and then studied with the light microscope while in liquid Epon. The equatorial regions are identified, then removed and embedded for examination using the electron microscope. This is the first successful total isolation of viable human spindles. The combined procedures allow correlation of recordings from the primary sensory endings with the fine structure of spindles from normal persons and from patients with neuromuscular disorders.

Notes: The sensory innervation of the mandibular stylets of the aphid Brevicoryne brassicae (L.) has been examined by electron microscopy. Two groups of sensory neurones are present in the mandible. Each has two neurones, one with a short dendrite extending into the base of the mandible and ending in the base and another with a long microtubular process which extends 500 m̈ down to the distal tip of the mandible. The two neurones are enclosed by an ensheathing cell comparable to the trichogen cell enveloping the group of neurones innervating pegs and hairs. This ensheathing cell is supported by extensive electron-dense filaments to form a scolopale and is embedded in the mass of stylet-forming cells at the base of the mandible. The inner segments of the dendrites are anchored to the ensheathing cell by desmosome junctions. Desmosome junctions also bind the microtubular outer segments of the short and long dendrite to each other. There is no evidence of a dendritic sheath enclosing the distal portion of the short dendrite which ends while still in the extracellular space within the ensheathing cell. The microtubular process of the long dendrite extends down the lumen of the mandible enclosed by a close-fitting extracellular sheath which penetrates and is attached to the cuticular wall of the mandible tip. Distally this sheath is thickened on one side. Deflection of the mandible would therefore deform the dendritic membrane asymmetrically because the thin walls of the sheath would bend more than the thick walls. This would exert an unequal mechanical strain on the dendritic membrane which could result in depolarization in response to deflection in a particular direction. The arrangement of the dendrites and their sheaths within the mandible is such that deflection to the right would distort one dendrite in the same way as deflection to the left would distort the other.

Notes: Ampullary receptor organs of African mormyrids consist of a cavity beneath the epidermis. The wall of the cavity contains embedded receptor cells and two types of supporting cells. A canal extends from the cavity to an opening at the surface. The lumen of the canal and the ampulla are filled with a jelly-like material and dense cylinders apparently secreted by two types of supporting cells. Flattened cells of the canal wall are joined by occluding junctions. Synapses between receptor cells and the afferent nerve fiber are characterized by a presynaptic dense body, but presynaptic vesicles were not observed. Degenerating receptor cells are occasionally seen among normal receptor cells in the base of the organ.

Notes: This paper examines the effect of early thymectomy on the subsequent development of lymphoid tissues in the toad, Xenopus laevis. At the time of thymic removal (8 days post-fertilization) all the lymphoid organ anlagen are at a rudimentary state of differentiation and contain few, if any, small lymphocytes. Despite the absence of any thymic tissue all thymectomized animals grew normally.Thymectomized larvae developed relatively normal lymphoid organs. However, lymphoid depletion was apparent in the splenic red pulp and in the pharyngeal ventral cavity bodies. Examination of the lymphoid organs of post-metamorphic Xenopus revealed reduction in spleen size following thymectomy. Lymphoid depletion was evident in the splenic red pulp of many thymectomized toadlets and reduction in proportion of white to red pulp was also noted in a few of these animals. Absence of the thymus had no apparent effect on the histology of the other lymphoid organs examined.

Notes: Extraocular muscles from representative species of vertebrate groups ranging from amphibians to the higher mammals were examined in serial histological sections for the presence of muscle spindles. These observations and data from the literature indicate that extraocular muscles of the pig, calf, sheep and other even-toed ungulates are richly supplied with well-defined spindles having a generous complement of intrafusal fibers distinguishable as nuclear bag and chain fibers. Spindles in human eye muscles are also numerous. In macaque and chimpanzee muscles a few poorly developed spindles were present in some, but not all, muscles. No encapsulated receptors were found in 20 other mammalian and submammalian species examined in this study. When present, spindles tended to be located in the zone of small muscle fibers found along the orbital surface of the muscle. Rectus and oblique muscles in all species had such a zone, so that its existence did not determine whether spindles would occur.

Notes: Gonadotrophic cells in the pars distalis of Anolis carolinensis often contain juxtanuclear concentrations of filaments with diameters intermediate in size (approximately 100 Å) between microtubules and microfilaments. Their size and their substructure, which gives them a tubular appearance when they are displayed in cross-section, appear to place these filaments in the “intermediate filament” category (Ishikawa et al., '68). In their juxtanuclear position in the intact animal, the intermediate filaments are collected in randomly-oriented tangles. In castrated specimens of Anolis, gonadotrophs degranulate and elongate. During this elongation, increased numbers of microtubules appear in orientation parallel to the long axis of the cell, and the 100 Å filaments reassemble in rod-like masses oriented parallel to the microtubules. This apparent distributional interaction may facilitate the elongation of the cell. Intimate physical associations between the intermediate filaments and secretory granules suggest that the filaments may act in the movement of the granules during the processes of degranulation and secretion.

Notes: The long antennal flagellum of Neoconocephalus ensiger is covered with many sharp-tipped hairs that appear to be non-innervated; thick-walled chemoreceptors, that may also have a tactile function; thin-walled chemoreceptors of several kinds and coeloconic chemoreceptors. All of the chemoreceptors are innervated by small groups of neurons. The first flagellar subsegment is unusual in that it bears a small protuberance on its latero-ventral surface. This marks the site of the attachment, internally, of a scoloparium containing about eleven scolopales in which the dendrites of some 23 sensory neurons terminate. The most distal subsegment lacks the scoloparium reported earlier for the grasshopper. No conspicuous difference between the antennae of males and of females was found.

Notes: The antennae of two species of thrips, Bagnalliella yuccae (Hinds) and Frankliniella tritici (Fitch), have been examined with the light and electron microscopes. The antennal flagellum of both species is provided with tactile hairs, thick-walled chemoreceptors and thin-walled chemoreceptors. In addition, B. yuccae, but not F. tritici, has a single coeloconic chemoreceptor on the dorsal surface of the pedicel. Observations were made on the fluids in the lumen of the antennae of E. yuccae in the living insect. The movement of the fluids probably has an important physiological significance.

Notes: The cervicothoracic muscles of nymphal and adult Euborellia annulipes (Lucas) are described, the former for the first time. In the adult, eight new muscles are identified, while the nymphs possess a further seven muscles that disappear at maturation or before. Otherwise the same muscles occur in nymphs as in adults, though some nymphal muscles are less clearly separated from one another than their adult homologs. The attachment sites of certain muscles show a number of slight differences between nymphs and adults. The work emphasizes the necessity of taking the immature musculature into account in assessing the muscular pattern represented in an insect order.

Notes: Some of the cytological characteristics of the hemocytes of the scorpion, Palamnaeus swammerdami, were studied. The morphological features of the arachnid hemocytes were observed to be similar to those of hemocytes of insects, millipedes and isopods. Jones' system of hemocyte classification was extended to the arachnid hemocytes. The six classes of hemocytes indentified in the scorpion correspond to prohemocytes, plasmatocytes, granular hemoocytes, cystocytes, spherule cells and adipohemocytes of insects. A cell type comparable to oenocytoids of insects and crustaceans is absent. The prohemocytes can be subdivided into four categories that probably represent the precursors of the major cell types. The cytological characteristics of the major cell classes and the occurrence of the miniatures of some of these major cell types support the concept of Jones (62) that these cell types might have different cell lineages and might not be capable of transforming into one another. Some of the prohemocytes, plasmatocytes and granular hemocytes were amoeboid. The nature of the granules and the vacuoles of plasmatocytes and granular hemocytes were compared with the granules and vacuoles of corresponding hemocytes of other arthropods. Cystocytes did not bring about any visible coagulation similar to their counterparts in millipedes and crustaceans. Plasmatocytes, granular hemocytes and spherule cells were observed to occur in conglomerates. The cell types noted in the present study were compared with the hemocytes of other arachnids.

Notes: The morphological features of the hemocytes of the crustacean Ligia exotica are similar to hemocytes of insects and millipedes. Jones system of hemocyte classification is extended to crustacean hemocytes. As in insects, seven classes of hemocytes, identified as prohemocytes, plasmatocytes, granular hemocytes, cystocytes, oenocytoids, spherule cells and adipohemocytes, occur. The prohemocytes can be subdivided into five categories that probably represent the precursor of major cell types. The structural and chemical features of other major cell classes are distinct and support the concept of Jones ('62) that these types might have different lineages and might not be capable of transforming into one another. Some of the prohemocytes, plasmatocytes and granular hemocytes are amoeboid. Cystocytes do not bring about any visible plasma coagulation similar to their counterpart in millipedes. Oneocytoids and adipohemocytes are rare. Plasmatocytes, cystocytes and oenocytoids occur in conglomerates, the significance of which is discussed. The cell types are compared with those of the hemocytes of other crustaceans. It is suggested that the nomenclature based on morphological characters is more suited for crustacean hemocytes than a nomenclature based on behavioural and physiological characters.

Notes: The biomechanical role of the mammalian clavicle and the functional significance of the aclaviculate condition were investigated. Shoulder movements in rats (Rattus norvegicus) with excised clavicles were compared to those of normal rats by biplanar plate radiography. Shoulder movements during walking of the claviculate American opossum (Didelphis marsupialis), and aclaviculate raccoons (Procyon lotor) and cats (Felis domestica) were compared by biplanar cineradiography.The mammalian clavicle, where present in its complete form, exerts both a “spoke” and a “strut” effect on shoulder movement. By maintaining a fixed distance between the acromion and manubrium, the clavicle ensures that relative movement between these structures is arcuate. Aclaviculate mammals, in contrast, have linear shoulder excursions that are nearly parallel or slightly oblique to the median plane, depending on the conformation of the thorax. Medial collapse of the shoulder in aclaviculate rats demonstrates that the clavicle is under compression, and thus acts as a strut.Reduction or loss of the clavicle, which has occurred independently in numerous mammalian phylogenies, has been regarded as an adaptation for greater shoulder movement and hence increased stride. However, on present evidence clavicular reduction in cursorial mammals appears to be more directly related to a linear excursion of the shoulder joint and a restriction of limb movements to a sagittal plane.

Notes: The tail of Teratoscincus scincus has dorsal scales that have tubercles on their dorsal and ventral surfaces. Sounds are produced when these rub past each other as the excited animal moves its tail. The relative movement of scales is intensified by caudal torsion. The frequencies of the sounds cover a range from 9 to 25 kops and thus, differ from those produced during vocalizations.

Notes: The locomotor function of the caudal muscle cells of ascidian larvae is identical with that of lower vertebrate somatic striated (skeletal) muscle fibers, but other features, including the presence of transverse myomuscular junctions, an active Golgi apparatus, a single nucleus, and partial innervation, are characteristic of vertebrate myocardial cells.Seven stages in the development of the compound ascidian Distaplia occidentalis were selected for an ultrastructural study of caudal myogenesis. A timetable of development and differentiation was obtained from cultures of isolated embryos in vitro.The myoblasts of the neurulating embryo are yolky, undifferentiated cells. They are arranged in two bands between the epidermis and the notochord in the caudal rudiment and are actively engaged in mitosis.Myoblasts of the caudate embryo continue to divide and rearrange themselves into longitudinal rows so that each cell simultaneously adjoins the epidermis and the notochord. The formation of secretory granules by the Golgi apparatus coincides with the onset of proteid-yolk degradation and the accumulation of glycogen in the ground cytoplasm.Randomly oriented networks of thick and thin myofilaments appear in the peripheral sarcoplasm of the muscle cells of the comma embryo. Bridges interconnect the thick and thin myofilaments (actomyosin bridges) and the thick myofilaments (H-bridges), but no banding patterns are evident. The sarcoplasmic reticulum (SR), derived from evaginations of the nuclear envelope, forms intimate associations (peripheral couplings) with the sarcolemma.Precursory Z-lines are interposed between the networks of myofilaments in the vesiculate embryo, and the nascent myofibrils become predominantly oriented parallel to the long axis of the muscle cell.Muscle cells of the papillate embryo contain a single row of cortical myofibrils. Myofibrils, already spanning the length of the cell, grow only in diameter by the apposition of myofilaments. The formation of transverse myomuscular junctions begins at this stage, but the differentiating junctions are frequently oriented obliquely rather than orthogonally to the primary axes of the myofibrils.With the appearance of H-bands and M-lines, a single perforated sheet of sarcoplasmic reticulum is found centered on the Z-line and embracing the I-band. The sheet of SR establishes peripheral couplings with the sarcolemma.In the prehatching tadpole, a second collar of SR, centered on the M-line and extending laterally to the boundaries with the A-bands, is formed. A single perforated sheet surrounds the myofibril but is discontinuous at the side of the myofibril most distant from the sarcolemma. To produce the intricate architecture of the fully differentiated collar in the swimming tadpole (J. Morph., 138: 349, 1972). the free ends of the sheet must elevate from the surface of the myofibril, recurve, and extend peripherally toward the sarcolemma to establish peripheral couplings.Morphological changes in the nucleus, nucleolus, mitochondria, and Golgi bodies are described, as well as changes in the ground cytoplasmic content of yolk, glycogen, and ribosomes.The volume of the differentiating cells, calculated from the mean cellular dimensions, and analyses of cellular shape are presented, along with schematic diagrams of cells in each stage of caudal myogenesis. In an attempt to quantify the differences observed ultrastructurally, calculations of the cytoplasmic volume occupied by the mqjor classes of organelles are included.Comparison is made with published accounts on differentiating vertebrate somatic striated and cardiac muscles.

Notes: Anolis embryos have limb buds at the time eggs are laid and require about 39 days to complete development at 28°C. Rathke's pouch is present at five days, and the subdivisions of the adenohypophysis are differentiated by ten days after oviposition. The cells of the rostral half of the pars distalis (PD) are derived from the anterior face of Rathke's pouch; cells of the caudal half from the posterior face. Lateral lobe cells differentiate on the lateral margins of the developing caudal PD, and knob-like outgrowths of this tissue attach to the walls of the diencephalon to form the pars tuberalis (PT). Subsequently, the cells of the PT lose their connection with the PD and become a pair of flattened oblong plaques. They reach maximal size in midincubation, and are gradually invaded by nervous elements and incorporated into the walls of the hypothalamus. Electron micrographs demonstrate that the embryonic PT is secretory.Ultrastructurally the pars intermedia (PI) and PD are composed of parenchymous secretory cells in a framework of stellate cells. Stellate cells surround the lumen of Rathke's pouch and are connected laterally by complex junctions that exclude the secretory cells from the luminal surface. They extend in sheet-like processes among the secretory cells to the outer margin of the gland where they form a partial sheath within the basal lamina around the secretory tissue. As development proceeds, the lumen becomes subdivided and the resulting reduced lumina are recognizable as the forerunners of the follicles of the adult adenohypophysis.The cells of the PI are differentiated into secretory or stellate cells halfway through incubation. At this time only half of the cells of the PD can be so classified. Four of the five granulated cell types described in the adult are recognizable by mid-incubation; the fifth cell type (prolactin cell) becomes distinguishable within ten days thereafter, and at hatching appears to be actively synthesizing secretory products.

Notes: The hydranth of the gymnoblastic hydroid Syncoryne tenella is invested by a cuticle approximately 530 mμ thick which is continuous with the periderm of the hydrocaulus. The ectodermal cells of the hydranth possess regularly spaced microvilli orientated with their long axis perpendicular to the ectodermal surface. The microvilli project into the cuticle, and probably serve to anchor the cuticle to the ectoderm. In the hydrocaulus the periderm is loosely applied to the ectoderm: in this region microvilli are absent from ectodermal cells. The periderm is a layered structure composed of finely filamentous material. No structural basis is found for the previously reported differential staining of peridermal layers in the hydrocaulus.

Notes: The nuchal organs of polychaetes from four different families (Nereidae, Nephtyidae, Phyllodocidae and Glyceridae) were examined with the light and electron microscopes. In each case, the organ consists of ciliated cells and primary sensory elements. The ciliated cells are similar to the cells of the adjacent epidermis but bear motile cilia. Primary sensory neurons are situated within the organs in Nephtyidae and Phyllodocidae, but are located within the brain in Nereidae and Glyceridae. Each sensory cell gives rise to a distal process which penetrates between the ciliated cells to form an apical sensory bulb bearing modified cilia. Apically these processes are lined with juxtamembranous plaques. The ciliated cells are innervated by efferent axons from the brain, and in Nereis the axons appear to be peptidergic. The elements comprising the nuchal organs closely resemble those of the vertebrate olfactory mucosa.

Notes: The male genital systems of two mysids, Archaeomysis grebnitzkii (subfamily Gastrosaccinae) and Neomysis awatschensis (subfamily Mysinae) are described. The testes of both species include a pair of central cords (spermatogonial cells), two sets of lateral sacs, and a set of dorsal-lateral spermatidic pouches in which spermiogenesis takes place. Mature sperm exit dorsally from the pouches into a common U-shaped seminal vesicle, the arms of which extend posteriorly as the right and left vasa deferentia.The emphasis of this study was on the follicle cell-spermatid relationship. Spermatids retain their own cell membranes as do the follicle cells. A bundle of sperm tails extends toward the follicle cell nucleus making several revolutions about the nucleus. Masses of rodlets occupy this tract with the spermatid tails. The tail consists of an outer cylinder with banding in a periodicity similar to collagen protein, and an inner cavity filled with a structureless, dark-staining material. Heads of the spermatozoa differ considerably between the two species. The elongate, reflexed head of Neomysis with its central filament joins the tail at an acute angle. The short cylindrical head of Archaeomysis with its anterior hood-like extension joins the tail directly. The distinctiveness of the sperm types might prove useful for taxonomic purposes. As noted by previous investigators, the number of spermatids per follicle cell shows specificity: Neomysis awatschensis has around 16 spermatids per follicle cell, Archaeomysis grebnitzkii about 100.

Notes: Relationships between the cribriform plate of the ethmoid, the olfactory bulb, and olfactory acuity were explored using material from 13 of the 17 bat families.All megachiropteran cribriform plates were entirely perforated. In contrast, microchiropteran plates showed distinct perforated portions dorsally and nonperforated portions ventrally. The plates of frugivorous species had more foramina than those of insectivorous ones. Bats with mixed dietary habits were intermediate. Our data suggest that the Chilonycterinae were originally frugivorous, and have only secondarily reverted to an insectivorous diet.Trend analyses show that wherever dietary preference appears to favor a more acute sense of smell, bulb diameter tends to be larger. In general, frugivorous bats tend to have bulbs exceeding 2 mm in diameter; insectivorous bats tend to have bulb diameters of 2 mm or less. The number of foramina in the plates and total cribriform plate area tends to increase as a function of bulb area, but the plate area the foramina occupied increases as a function of bulb volume. The ratio of the size of the bulb to the size of the cerebral hemisphere does not predict olfactory acuity in bats.

Notes: Mast cells were demonstrated in eight species of snakes, using special fixation techniques to prevent solubilization of cytoplasmic granules. Toluidine blue O and azure A were the major stains and observations were made under light microscope including cytophotometric analysis.The mast cells of snakes were shown to be relatively small (7-11 μ in diameter) when compared to mast cells of a lizard (8-15 μ), dog and rat (9-15 μ).Among the various organs examined, mast cells were particularly numerous in the mesentery, tongue, underneath the serosa of the digestive tract and in the heart, between muscle fibers and in the epicardium.Although under the light microscope some snake mast cells seemed to be orthochromatically stained, when analysed by cytophotometry they were demonstrated to be actually metachromatic.Snake mast cells granules were demonstrated to have an amphoteric behavior, since they were stained with both basic (toluidine blue O and azure A) and acid dyes (eosin and ponceau-acid-fuchsin).

Notes: The number, location, size, shape and microstructure of the parathyroid glands of Agama agama agama, Hemidactylus brooki angulatus and Pytodactylus hasselquisti hasselquisti was investigated using approximately 250 specimens of each species from the Zaria area of Nigeria.Only parathyroid III was found. Additional patches of tissue in Hemidactylus, though possibly parathyroid IV, are considered to be derived from parathyroid III. It was found that the amount of parathyroid tissue per gram of body weight was similar in the three species used, and that females had more parathyroid tissue than males. The same situation seems possible in other species.The structure of the parathyroid glands could not be related to taxonomic grouping within the Sauria, but the general picture was found to be more similar to that of birds and mammals than to that of amphibians.

Notes: Retinal projections were studied experimentally in the Northern water snake using modifications of the Nauta silver impregnation technique. Contralaterally, the retina projects to nucleus geniculatus lateralis pars dorsalis and pars ventralis, nucleus lentiformis mesencephali and nucleus geniculatus pretectalis. A sparse projection was also observed to nucleus ovalis. An additional afferent thalamic projection to nucleus ventrolateralis was found in two cases. The retina projects ipsilaterally to the dorsolateral portion of nucleus geniculatus lateralis pars dorsalis, and sparsely to nucleus lentiformis mesencephali and nucleus geniculatus pretectalis. Nucleus posterodorsalis receives dense bilateral retinal projections. Contralaterally, the retina also projects to the superficial layers of the tectum (layers 8-13 of Ramón) and to nucleus opticus tegmenti. Armstrong's findings that the retinal projections in Natrix are qualittatively similar to those in lizards were confirmed. However there are marked quantitative differences among the various pathways and their corresponding nuclei. These differences are particularly striking in comparing the visual projections to the dorsal thalamus, the retino-tecto-rotundal and the retino-geniculate systems. The first is reduced in volume and the second is markedly increased in volume in comparison with lizards. These data lend support to the theories of Walls that snakes evolved from fossorial lizards and of Underwood that the eyes of these lizards underwent reduction but not complete degeneration. Qualitatively the retinal projections are conservative among lizards and snakes, but a history of reduction of these pathways in ancestral snakes with a selective increase in the retino-geniculate system as a surface niche was reattained is reflected in the anatomy of this ophidian visual system.

Notes: Fine structure of the torus semicircularis of the loach, carp, common eel and rainbow trout was studied by light and elecron microscopy. The torus semicircularis of each species is divided into four layers. The subependymal first layer comprises numerous unmyelinated fibers and their terminals which contain cored vesicles. The second and the third layers are composed of small cell bodies and their dendrites respectively. These layers develop equally in the four species and contain the usual axodendritic synapses. On the other hand, the fourth layer varies in different species. The mediumsized cells in this layer, which are inferred to be of the same origin as the small cells from their configuration and size, show differences in lamination in each species. Compared with the usual axodendritic synapse of the small cells, the medium-sized cells have quite different synaptic patterns, which include inhibitory and electrical as well as the usual excitatory chemical synapses. From these findings, the medium-sized cells are surmized to receive sound of different degrees of intensity from that received by the small cells, which may have an effect on feeding behaviors of the species. In the deepest portion of the torus semicircularis of all species, there are large multipolar cells on which numerous axon terminals synapse in much the same way as they do on the medium-sized cells. These findings suggest that the synaptic patterns in the torus semicircularis may depend not on the receptive cells in each layer but on the various characteristics of the afferent fibers.

Notes: Abdominal extra-adrenal chromaffin tissue, or paraganglia, was examined at the ultrastructural level to elucidate the innervation of this adrenal medullary homologue. Paraganglia display unmyelinated nerve fibers surrounded by Schwann cell cytoplasm. These nerves are separated from the paraganglion Type I (granule-containing) cells by cytoplasmic projections of paraganglion Type II (satellite) cells. However, serial sections show that the nerves eventually make synaptic contact with the Type I cell. At the axon-chromaffin cell junction, only the outer aspect of the nerve is covered by the satellite cell. The presynaptic endings contain numerous synaptic vesicles, mitochondria and glycogen particles. The vesicles are predominantly of the clear-cored variety, but a few possess centers which are elecron opaque. The pre- and postsynaptic membranes are separated bya subsynaptic space and occasionally exhibit the membranal densities usually associated with synaptic areas. These ultrastructural studies establish definite evidence that abdominal paraganglion cells are innervated.

Notes: The gland cells of Lyonet's gland, which is accessory to the silk gland in the silkworm larva, is characterized by the presence of complicated canaliculi bearing microvilli on their inner surface, large numbers of mitochondria and remarkably convoluted basal plasma membrane. On the other hand, the cell lacks the well-developed cytoplasmic membrane system such as rough- and smooth-surfaced endoplasmic reticula and Golgi bodies, though free ribosomes are numerous. Secretory vesicles are absent, and the canaliculi contain no dense material. From such ultrastructural observations, it was suggested that a possible role of the gland may be the exchange of the small molecules such as water and ions, rather than the hitherto supposed secretory role of a cementing sunstance of silk proteins. The lumen of the proximal part of the glandular duct contains a kind of proteinaceous substance which can be demonstrated histochemically and is regarded as similar to one of the silk proteins in the silk gland, not to the real product of the Lyonet's gland.

Notes: Specimens, representative of each of the major taxa of mosquitoes, were fixed in copula and the external genitalia examined by scanning electron microscopy. The periphery of the basin-like everted aedeagus of Aedus aegypti precisely matches that of the everted atrial membrane of the female. These structures are appressed during coitus and sealed by pressure of the paraprocts, aedeagal pouch and proctiger. When everted, the aedeagus of male Culex pipiens reveals a ridged dome that surrounds the genital opening. This dome seals itself laterally into a gutter formed by pad-like extensions of the female's genital lips and is sealed dorsally by pressure of the aedeagal apodeme. The aedeagus of another culicine species, Wyeomyia smithii, bears the gonopore at the apex of a spined tube. This tube is inserted between the female's genital lips and is sealed within the genital atrium. The aedeagus of the toxorhynchitine species Toxorhynchitis brevipalpus is immobile and is inserted deep within the genital atrium of the female where it is sealed by pressure of the atrial walls. Males of each of these mosquitoes deliver a mixture of semen and sperm to the copulatory bursa of the female. After withdrawal of the aedeagus, sperm is transferred to the spermathecae.In contrast, sperm of Anopheles quadrimaculatus are delivered directly to the spermathecal duct. The tube-like aedeagus is positioned by its leaflets during sperm transfer and is driven deep into the atrium, where a mixture of semen and sperm is ejaculated.The significance of mechanical barriers to mating between species is discussed.

Notes: The gross and microscopic anatomy of the venom producing parotoid glands of Bufo marinus has been studied by light and electron microscopy and reactions for the presence of glycoprotein and mucopolysaccharides, the catechollamines, 5-hydroxytryptamine or dopamine, glucose-6-phosphatase, adenosine triphosphatase and the steroid nucleus and cholesterol and its esters have been performed. The gland is composed of numerous individual lobules, each lobule surrounded by a double cell layer. The interior surface of the outer layer is thrown into small cytoplasmic projections which traverse an intercellular space and interdigitate with microvilli formed by the outer plasmalemma of the inner layer. The outer layer resembles smooth muscle-like cells, is rich in adenosine triphosphatase, contains many pinocytotic vesicles and various organelles and may function in some aspect of venom synthesis, active cellular transport and contraction in the discharge of the secretory product. The inner layer shows a positive chromaffin reaction, contains various organelles, appears devoid of a plasmalemma on its inner surface and is involved in venom formation and release via an apocrine type of secretion. The intercellular space is rich in PAS positive materials, while the secretory product, itself, demonstrates a positive chromaffin reaction. The significance of these findings is discussed.

Notes: The synganglion of Dermacentor variabilis Say is a single nerve mass, condensed around the esophagus and within the periganglionic sinus of the ciculatory system. Protocerebral, cheliceral (including stomodeal bridge), and pedipalpal ganglia lie in the pre-esophageal portion of the nerve mass and bear optic, cheliceral, and pedipalpal nerves respectively. The unpaired stomodeal and the recurrent nerve which forms the hyper-esophageal ganglion arise from the stomodeal bridge. Paired primary and accessory nerves to the retrocerebral organ complex have mixed protocerebral-cheliceral origins. Pedal ganglia (including ventral olfactory lobes of pedal ganglia I) and composite opisthosomal ganglion lie in the post-esophageal nerve mass and bear pedal nerve trunks and two pairs of opisthosomal nerves respectively.Internally, the synganglion consists of cellular rind and fibrous core. A welldefined neurilemma with a laminar matrix covers nerve mass and peripheral nerves. The rind contains the somata of ganglionic neurons and ensheathing glial cells and is restricted to the synganglion mass. It is limited by two specialized glial layers, the external perineurium and internal subperineurium. Discrete glomerular formations are present within the protocerebrum and olfactory lobes. Olfactory glomeruli located in pedal ganglia I are associated with a pair of globuli cell groups.Possible physiological relationships between anatomical specializations of the synganglion, extraneural sinuses and circulating hemocytes are considered. The evolutionary significances of condensation in the stomatogastric neuropile regions and throughout the synganglion, together with the simplification and loss of glomerular formations, are discussed.

Notes: The intraspecific mean length of medullary cones in avian kidneys is analogous to medullary thickness in the mammalian kidney. Hence, relative medullary thickness (based upon kidney volume) can be calculated for birds as was done in mammals years ago. Comparative figures are given for 26 species from nine avian orders. The organizational pattern of cortex and medulla in the bird kidney is reviewed, and a simplified diagram of this relationship is presented. With some exceptions, urine concentrating ability and relative medullary thickness are directly proportional in mammals. Contrarily, no similar trend was evident in birds when current information on water economy was compared to relative medullary thickness in various species. There are a number of factors (such as the respective functional roles of reptilian and mammalian-type nephrons, interspecific variations in ion transport, etc.) which require study before the significance of relative thickness in the avian medulla can be evaluated more thoroughly.

Notes: The stylocyte (Gr. stylos; pillar) of Corvomeyenia carolinensis Harrison (Spongillidae), a previously undescribed proiferan cell type, was examined using phase contrast microscopy, histochemistry and electron microscopy. The stylocyte, an anucleolate amoebocyte, is characterized by a rhomboidal intranuclear crystal. The crystal, lacking an investing membrane, is embedded directly into the nucleoplasm. It is homogenous with no demonstrable crystalline subunits. Histochemical studies suggest that the crystal is proteinaceous, containing no DNA or RNA. Cytoplasmically, the stylocyte contains promienent homogenous smooth membrane-bound inclusions which contain high levels of neutral (PAS-positive) and polycarboxylated mucopolysaccharides but low levels of glycogen and no significant phosphatase activity. The granular endoplasmic reticulum is poorly developed. Correspondingly, with various histochemical methods, little or no cytoplasmic RNA is demonstrated. Because electron microscopic studies of C. carolinensis indicate the probable absence of viral inclusions in the sponge and because the crystal contains no histochemically demonstrable nucleic acid, the evidence appears to suggest that the crystal neither represents an assemblage of mature virus units nor a virus-induced structure. The stylocyte cell type may play a role in nutrient cycling in C. carolinensis with the crystal acting either as a site of protein storage or as an excretory product.