Size Of Microvilli Research Articles

Effect of white spot syndrome virus on the activity of immune-related enzymes in the red claw crayfish (Cherax quadricarinatus)

In this study, we explored the pathogenic effects of white spot syndrome virus (WSSV) and effects of yeast cell wall in the red claw crayfish, Cherax quadricarinatus, by investigating the activity of enzymes related to innate immune function following artificial infection of immunized and non-immunized crayfish. Our results reveal that the activity of four enzymes, phenoloxidase (PO), peroxidase (POD), superoxide dismutase (SOD) and lysozyme (LSZ), increased in the hepatopancreas and antennal gland of C. quadricarinatus 6 – 24 hours after exposure to WSSV. After, activity levels of these enzymes decreased rapidly, such that 72 h post-exposure the activity of the enzymes in WSSV-infected crayfish were significantly lower than those of the control individuals (except for LSZ). Interestingly, we found that immunization with yeast cell wall before challenge with WSSV conferred an immune protection rate of 51.86% at 7 days post-infection, demonstrating that yeast cell wall could improve immune-related enzyme activity in the crayfish and enhance the anti-viral defenses of this species. Morphological examination by transmission electron microscopy revealed significant damage in the hepatopancreas and antennal glands of infected crayfish. WSSV infection caused damage to the epithelium of the hepatopancreas and antennas and reduced the number and size of microvilli. In addition, mitochondria morphology changed following infection, with parts of the cristae diminished leaving large vacuoles. Moreover, the dictyosome morphology changed, the lysosome membranes ruptured, and heterochromatinized nuclei could be seen in cells with ruptured nuclear membranes. Despite this no WSSV particles appeared in the hepatopancreas or in the antennal gland.

The effects of activated omental extract on nuclear and cytoplasmic in vitro maturation of rat oocytes.

Objective:The role of growth factors, including vascular endothelial growth factor of activated omentum on mitosis is clearly known, though not on all the aspects of in vitro oocyte maturation. This study was designed to assess the effect of activated-omental extract (AOE) on in vitro maturation (IVM) of rat cumulus-oocyte complexes (COCs).Materials and Methods:In this experimental study, the COCs were incubated in Ham’s F-10 supplemented with either 20% AOE, 20% fetal bovine serum (FBS) or serum-free media. Post-culture COCs were studied according to the cumulus cells (CCs) expansion, nuclear maturation and cytoplasmic maturation. Cumuli expansion was evaluated by inverted microscope without staining; nuclear maturation was assessed by aceto-orcein staining (light microscope) and cytoplasmic maturation was also observed by TEM.Results:Expansion of CCs and nuclear maturation of the oocytes in in vitro for 24 hr was significantly higher in AOE- and FBS-supplemented groups (P=0.000 and 0.013) and (P=0.004 and 0.014), respectively, compared to serum-free group. At ultra-structural level, after 24 hr, both FBS and AOE-supplemented media showed uniformly wide perivitelline space (PVS). After 12 hr, the cortical granules were found in the oocytes cultured in FBS and AOE-supplemented media. Within 24 hr, both granules and mitochondria were large without any detectable topographic tendency across the ooplasm. In AOE and FBS-supplemented oocytes, the number and size of microvilli were more than those in serum-free one.Conclusion:Although AOE supplementation induced a higher rate of the CCs expansion, and resuming meiosis, it was not as potent as FBS to provide cytoplasmic maturation of rat oocytes.

TBT effects on the development of intersex (ovotestis) in female fresh water prawn Macrobrachium rosenbergii.

The impact of tributyltin (TBT) on the female gonad and the endocrine system in Macrobrachium rosenbergii was studied. Prawns were exposed to environmentally realistic concentrations of 10, 100, and 1000 ng/L of TBT for 6 months. Dose dependent effects were noticed in TBT exposed prawns. At 1000 ng/L TBT caused ovotestis formation (formation of male germ cells in ovary). Presence immature oocytes, fusion of developing oocytes, increase in interstitial connective tissues, and its modification into tubular like structure and abundance of spermatogonia in the ovary of TBT treated prawns. The control prawn ovary showed normal architecture of cellular organelles such as mature oocytes with type 2 yolk globules, lipid droplets, normal appearance of yolk envelop, and uniformly arranged microvilli. On the other hand, type 1 yolk globules, reduced size of microvilli, spermatogonial cells in ovary, spermatogonia with centrally located nucleus, and chromatin distribution throughout the nucleoplasm were present in the TBT treated group. Immunofluorescence staining indicated a reduction in vitellin content in ovary of TBT treated prawn. Moreover, TBT had inhibited the vitellogenesis by causing hormonal imbalance in M. rosenbergii. Thus, the present investigation demonstrates that TBT substantially affects sexual differentiation and gonadal development in M. rosenbergii.

Histological, ultrastructural and biochemical studies on the kidney of mice treated with Carthamus tinctorius L. extract.

Carthamus tinctorius L. (C. tinctorius) is used as a food additive but also has medicinal applications. The present work was designed to investigate its probable side effects on the histology and function of the kidney in the mice. Sixty adult Balb/C mice were randomly distributed into one control and three experimental groups. The control group received only distilled water, while experimental groups were administered intraperitoneally C. tinctorius at doses of 0.7, 1.4, and 2.8 mg/kg for 49 consecutive days. In the end of experiments after blood sampling, the biochemical analyses of plasma were performed. Tissue samples were also taken and structural alterations were examined using light and electron microscopes. There were histological changes included decreasing in the diameter of glomerules, increase of proximal tubular lumen, tubular necrosis, leuckocyte infiltration, and massive congestion in the kidney of the 1.4 and 2.8 mg/kg C. tinctorius groups. Moreover, ultrastructural study revealed destruction of the glomerular basement membrane, shrinkage of podocyte΄s nucleus, and reduction in the number and size of microvilli in epithelial cells of renal tubules. Furthermore, the levels of creatinine in the plasma of 1.4 and 2.8 mg/kg C. tinctorius groups showed a significant increase in comparison with the control group (p<0.05). It is concluded that C. tinctorius extract exposure at doses of 1.4 and 2.8 mg/kg has harmful effects on the renal tissue and therefore, popular consumption of this plant should be reconsidered.

Biochemical and structural changes of the kidney in mice exposed to phenol

Aim: To investigate the histology and function of the kidney in mice exposed to different concentrations of phenol through the gavage method for 10 consecutive days. Materials and methods: Forty female BALB/c mice were selected and randomly divided into 1 control group and 3 experimental groups. The control group was administered distilled water through the gavage method, while the experimental groups received daily doses of 80, 180, and 320 mg/kg of phenol, respectively. After 10 days, blood samples were collected and the sera were analyzed biochemically. Renal tissue samples were also taken and histopathological changes of the kidneys were examined using optical and electron microscopes. Results: No significant differences were found in the serum levels of sodium, potassium, chloride, bicarbonate, or total protein in all of the phenol-treated mice in comparison with the control group. The levels of creatinine and blood urea nitrogen and the activity of alkaline phosphatase in the sera of the phenol-treated mice showed a significant increase in comparison with the control group (P < 0.05). Histological changes including renal tubules necrosis, interstitial lymphoplasmacytic nephritis, and hyperemia were observed. The ultrastructural changes included reduction in the number and size of microvilli in the epithelial cells of the proximal convoluted tubules (PCTs), deformation and shrinkage of the nuclei, malformation of the mitochondria and folding of the cytoplasm in the epithelial cells of the PCTs, dilation of the urinary space in the renal corpuscles, and formation of endothelial electron-dense deposits in the basement membranes of the glomeruli. Conclusion: Based on the findings, it is concluded that the observed significant increases of serum creatinine levels, blood urea nitrogen levels, alkaline phosphatase activity, and histopathological changes in the kidneys of phenol-treated mice indicate tissue injury. These findings suggest that treatment with different concentrations of phenol may cause nephrotoxicity in mice.

Surface characteristics of isopod digestive gland epithelium studied by SEM

The structure of the digestive gland epithelium of a terrestrial isopod Porcellio scaber has been investigated by conventional scanning electron microscopy (SEM), focused ion beam-scanning electron microscopy (FIB/SEM), and light microscopy in order to provide evidence on morphology of the gland epithelial surface in animals from a stock culture. We investigated the shape of cells, extrusion of lipid droplets, shape and distribution of microvilli, and the presence of bacteria on the cell surface. A total of 22 animals were investigated and we found some variability in the appearance of the gland epithelial surface. Seventeen of the animals had dome-shaped digestive gland "normal" epithelial cells, which were densely and homogeneously covered by microvilli and varying proportions of which extruded lipid droplets. On the surface of microvilli we routinely observed sparsely distributed bacteria of different shapes. Five of the 22 animals had "abnormal" epithelial cells with a significantly altered shape. In three of these animals, the cells were much smaller, partly or completely flat or sometimes pyramid-like. A thick layer of bacteria was detected on the microvillous border, and in places, the shape and size of microvilli were altered. In two animals, hypertrophic cells containing large vacuoles were observed indicating a characteristic intracellular infection. The potential of SEM in morphological investigations of epithelial surfaces is discussed.

Microvillar Size and Espin Expression in Principal Cells of the Adult Rat Epididymis Are Regulated by Androgens

Principal cells of the epididymis are the most prominent cell type and are noted for an apical cell surface studded with microvilli. The latter contain channel proteins that condition the microenvironment of epididymal lumen and promote sperm maturation; however, the regulation of the structure and integrity of microvilli is not well known. Espins are a family of proteins implicated in microvillar growth. The objectives of this study were to assess the regulation of espin in epididymal principal cells both in vitro and in vivo. Treatment of immortalized rat caput epididymal (RCE) cells with increasing doses of a homogenized testicular extract revealed a dose-dependent increase in the size of microvilli. Reverse transcriptase-polymerase chain reaction (RT-PCR) of adult rat epididymal RNA using espin-specific primers indicated the presence of a band at about 290 base pairs (bp) in all regions. Western blot analysis using affinity-purified espin antibody confirmed the presence of an approximately 110-kDa band in the epididymis, corresponding to espin isoform 1. In adult rats, immunocytochemistry revealed espin expression over principal cells. In orchidectomized rats, espin expression was significantly reduced, whereas ligation of the efferent ducts resulted in a decrease of espin expression but not to the extent of orchidectomy. The fact that espin expression was restored to control levels in orchidectomized rats supplemented with high levels of testosterone indicated that its expression was dependent on androgens and not on other lumicrine factors derived from the testis. Taken together, these data indicate that espin is expressed in the epididymis and is regulated by androgens.

Deep-apical tubules: dynamic lipid-raft microdomains in the brush-border region of enterocytes.

The brush border of small intestinal enterocytes is highly enriched in cholesterol- and glycosphingolipid-containing membrane microdomains, commonly termed as lipid 'rafts'. Functionally, transcytosis of IgA and exocytosis of newly made brush-border proteins in enterocytes occur through apical lipid raft-containing compartments, but little is otherwise known about these raft microdomains. We therefore studied in closer detail apical lipid-raft compartments in enterocytes by immunogold electron microscopy and biochemical analyses. Novel membrane structures, deep-apical tubules, were visualized by the non-permeable surface marker Ruthenium Red in the brush-border region of the cells. The surface-connected tubules were labelled by antibodies to caveolin-1 and the glycolipid asialo G(M1), and they were sensitive to cholesterol depletion by methyl-beta-cyclodextrin, indicating the presence of raft microdomains. Deep-apical tubules were positioned close to the actin rootlets of adjacent microvilli in the terminal web region, which had a diameter of 50-100 nm, and penetrated up to 1 microm into the cytoplasm. Markers for transcytosis, IgA and the polymeric immunoglobulin receptor, as well as the resident brush-border enzyme aminopeptidase N, were present in these deep-apical tubules. We propose that deep-apical tubules are a specialized lipid-raft microdomain in the brush-border region functioning as a hub in membrane trafficking at the brush border. In addition, the sensitivity to cholesterol depletion suggests that deep-apical tubules function as a cell-surface membrane reservoir for cholesterol and for rapid adaptive changes in the size of microvilli at the brush border.

Pyruvate prevents ischemia-reperfusion mucosal injury of rat small intestine

Since reactive oxygen intermediates (ROI, or free radicals) have been implicated in the pathogenesis of ischemia-reperfusion injury of the small bowel, we evaluated the pretreatment effect of pyruvate, a 3-carbon compound recently shown to inhibit superoxide production, on reperfusion mucosal injury in the rat. The small bowel of the ACI rat (n = 6) was divided into 2 5-cm segments, and 10 mL of a liquid diet containing pyruvate (0.32 g) or placebo (0.26 g) was instilled into the lumen of one of the segments for 10 minutes. The bowel was then made completely ischemic for 45 minutes by clamping the superior mesenteric artery, which was followed by 60 minutes of reperfusion. The production of ROI in bowel biopsy samples, estimated by luminol-enhanced chemiluminescence, was at least 80% decreased in the segment containing pyruvate compared with placebo immediately after ischemia (time 0), and compared with 30 and 60 minutes of reperfusion (P < 0.05 for each time point). After 60 minutes of reperfusion, the bowel segment containing the placebo diet showed villus sloughing with destruction of lamina propria and crypts, and mucosal neutrophil infiltration had increased by 80%. Electron microscope evaluation revealed a reduction in number and size of microvilli, dilatation of intercellular spaces, and intracellular vacuoles. The bowel segment containing pyruvate showed the villi and crypts to be intact, without enhanced neutrophil infiltration. Pyruvate pretreatment of the rat small bowel inhibits postischemic reperfusion mucosal histologic injury, neutrophil infiltration, and ROI production.

Cyclic alterations in rhesus monkey endometrium by scanning electron microscopy.

The present study was undertaken to correlate the surface topography of endometrium with altered concentrations of circulating steroids during different phases of the artificially-induced menstrual cycle. Scanning electron microscopy demonstrated that oestradiol during the oestrogenic phase induces an increase in the number of ciliated cells and the size of microvilli; by contrast, progesterone, in addition to inducing secretory activity in non-ciliated cells, had a negative effect on oestradiol-dependent morphological characteristics of ciliated cells, causing a reduction in cell number and deciliation, and inducing drooping of cilia during the progestogenic phase of the artificially-induced menstrual cycle. In addition, surface and glandular epithelial cells both actively participate in restoration of the endometrial surface during the menstrual phase, an event which parallels endometrial shedding.

DNA, protein, and plasma-membrane incorporation by arrested mammalian cells.

Incorporation of DNA, protein, and plasma membrane during blockage by aphidicolin or by doxorubicin was studied by flow cytometry and electrorotation of three cell lines (mouse-myeloma Sp2/0-Ag14, hybridoma H73C11, and fibroblast-like L929 cells). Drug-mediated arrest at the G1-S boundary (aphidicolin) or in G2/M (doxorubicin) did not arrest synthesis of either protein or total membrane area, the increases in which outstripped growth in cell volume and apparent cell area, respectively. Measurements of membrane capacity in normal and hypo-osmotic media showed that the drugs had not changed the fundamental bilayer, but that an increase in the number or size of microvilli must have occurred. Aphidicolin-arrested cells withstood hypo-osmotic stress better than untreated cells could, indicating that the membrane excess can be utilized as a reserve during rapid cell expansion. Hypo-osmotically treated cell populations exhibited only about half the coefficient of variance (CV) in membrane properties of cells at physiological osmolality. Populations of arrested cells exhibited the same high CV as asynchronous cells, indicating that chemical arrest does not give uniformly villated cell populations. However, the lowest CV values were given by some synchronized (aphidicolin-blocked, then released) populations. Removal of aphidicolin allowed most cells to progress through S and G2, and then divide. During these processes, the membrane excess was reduced. After removal of doxorubicin, the cells did not divide: some continued protein synthesis, grew abnormally large, and further increased their membrane excess. Membrane breakdown by electric pulsing (3 x 5kV/cm, 40 microseconds decay time) of aphidicolin-synchronized L cells in G2/M led to a 22% loss of plasma membrane (both the area-specific and the whole-cell capacitance were reduced), presumably via endocytosis-like vesiculation.

Response of adult murine uterine epithelium to 50% methoxychlor

This study was designed to assess the response of uterine epithelia of adult mice to a 4-week exposure of 50% methoxychlor (MXC) to ascertain whether significant changes were induced by 50% MXC that might compromise future implantation. Sexually mature virgin female mice were exposed to 0.1, 0.5, 1.0, 2.5, or 5.0 mg MXC via oral gavage for 5 consecutive days for 4 weeks. Controls received either sesame oil or 25 μg estradiol-17β (E-17β) also by gavage. At sacrifice, segments from each uterine horn were prepared for morphometric studies or for transmission electron microscopy. Results revealed a dose-dependent increase in the heights of uterine epithelial cells. Epithelial cell heights of the two groups treated with the highest doses of the pesticide were similar to that of the E-17β-treated group. Electron microscopy revealed increased vacuolization and swelling of mitochondria in cells of the 2.5 and 5.0 mg treated groups when compared to either of the control groups. In addition, there were effects on the number and size of microvilli in the uterine epithelial cells. The present study clearly demonstrates that a 4-week exposure of adult female mice to 50% MXC elicits significant estrogenic and toxic effects on the uterine epithelium.

Fine structure of adrenal cortex in rats harbouring a medullary thyroid carcinoma transfected with a corticotrophin-releasing hormone cDNA expression vector

We report the light microscopic, transmission and scanning electron microscopic features of the adrenal cortices in rats bearing a medullary thyroid carcinoma cell line transfected with a corticotrophin-releasing hormone (CRH) cDNA expression vector. The animals had elevated CRH, ACTH and corticosterone blood levels, involuted thymuses and markedly enlarged adrenal glands with prominent lipid-depleted cortices and dilated congested capillaries, similar to those of animals treated with ACTH. Using electron microscopy it was found that the enlarged fasciculata and reticularis zones were composed of large, compact cells with abundant smooth endoplasmic reticulum, prominent Golgi complexes, increased number of large mitochondria with focal loss of cristae and cavitation of the internal compartments, numerous lysosomes and prominent elongated microvilli. In addition, small cytoplasmic fragments were seen within the capillary lumina; these structures resembled microvilli that were apparently detached from adrenocortical cells and entered the blood stream via discontinuous endothelium of dilated capillaries. By scanning electron microscopy it was found that the cells had bulging surfaces with scattered pits and numerous long microvilli pointing in different directions. This animal model allows analysis of the effects of protracted CRH excess resembling tumoural CRH-dependent Cushing's syndrome in human patients. Our findings call attention to the role of microvilli in adrenocortical secretion. The increased number and size of microvilli has been thought to lead to an increase in the surface area of adrenocortical cells, thereby facilitating hormone discharge. The detachment of microvilli from adrenocortical cells may represent a form of apocrine secretion and may contribute to hypercorticosteronaemia in CRH excess.

Intestinal adaptation following jejuno-ileal bypass

The changes in functional and excluded loops were studied in two groups of patients at intervals up to 5 years after jejuno-ileal bypass. Macroscopic and histological observations confirmed that the compensatory increase of the absorbing surface of the functioning loop occurs, with an increase in length and width of the loop, hypertrophy of villi and microvilli, and increase in number and geometrical surface of the villous cells. In the excluded intestinal loop, atrophy occurs, evidenced by the reduction in number and size of microvilli, even if the height of villi may appear normal. The bacteriological studies of the functioning and excluded loops show bacterial colonization, which was not constant over the course of time.

Polysaccharide Complexes in Full-Grown Oocytes of the Newt, Pleurodeles, and Changes in their Distribution During Progesterone-Induced Maturation: (glycogen granules/oocyte maturation/polysaccharide complexes/urodele amphibian).

Immature full-grown oocytes of Pleurodeles waltlii contain large amounts of small electron-dense polysaccharidic granules. These granules lack a limiting membrane, and have a dense but heterogeneous matrix and an apparent diameter of 24-36 nm. Their structure, organization and distribution strongly suggest that they are glycogen granules. On the other hand, mature oocytes both after oviposition or 22-24 hr after in vitro progesterone stimulation contain no polysaccharide granules or complexes. During the first 9-10 hr after hormonal stimulation, granules were abundant and present both individually and as large strands occupying most of the space between the organelles. Granules were frequently found packed together and arranged in regularly arrayed stacks within large subcortical ant cortical vacuoles. Between 4 and 6 hr after progesterone addition, oocytes released the contents of vacuoles to the outside. Between about 11 and 14 hr after progesterone addition, oocytes still contained large amounts of polysaccharide complexes, but the vacuoles were empty. From about 15 hr after progesterone treatment until the end of maturation, the complexes progressively disappeared from the cytoplasm, coincident with the detachment of the follicle cell layer from the oocytes and a reduction in the number and size of microvilli.

Surface topography of mouse eggs before and after insemination

AbstractThe surface configuration of zona‐free mouse ovarian eggs before and after germinal vesicle breakdown (GVBD) and of tubal eggs before and after insemination was studied by scanning electron microscopy. The surface of germinal vesicle‐intact eggs was characterized by uniformly distributed, dense (2–3μm2 and slender (0.1 × 0.8μm) microvilli. Following GVBD, the mouse oolemma underwent dramatic changes which persisted essentially unmodified in uninseminated tubal eggs. These changes consisted of an apparent conversion of the oolemma from a microvillar to a smooth or ruffled configuration with approximately two ruffle‐like micro‐projections (0.6 × 0.4 μm) perμm2 of surface. In most eggs, both ruffled and smooth configurations ere present, creating dramatic polarities in surface topography similar to those documented previously by TEM [Nicosia et al, 1977]. Following insemination and presumed sperm–egg fusion, microvilli reappeared either from smooth areas or from the upper edge of ruffled microprojections. Zona removal appeared to induce limited reduction in the size of microvilli in some eggs. The present results emphasize the labile and dynamic nature of the egg surface and suggest a close relationship among nuclear, cytoplasmic, and surface events during the final stages of egg maturation and during fertilization.

A scanning electron microscopic study on the fractured rat parietal cells in resting state and after stimulation with tetragastrin.

Parietal cells in the rat gastric mucosa fractured by freeze cracking methods under resting (control) state and tetragastrin stimulation were studied by field emission scanning electron microscopy. The structures thus revealed were compared with those studied by transmission electron microscopy. In the fractured cytoplasm, intracellular canaliculi lined by numerous microvilli invaginated deeply towards the basal cytoplasm. Tubulovesicles appeared as many small holes about 0.05mu in diameter and were distributed predominantly in the apical or pericanalicular cytoplasm. Some tubulovesicles directly opened into the secretory canaliculi. Occasionally, tiny microvilli appeared in tubulovesicles. After being stimulated for 30 min with tetragastrin, the secretory canaliculi of parietal cells became enlarged and there were a concomitant increase in both the number and size of microvilli. Tubulovesicles also were increased in size and number and the tiny microvilli in them were also increased. The tubulovesicles were enlarged presumably as a result of membrane fusion between contiguous tubulovesicles. It was found that the enlargement of the secretory canaliculi was the result of fusion of the membrane of a single tubulovesicle or a confluence of tubulovesicles to that of the secretory canaliculus and the successive disappearance of the fused membrane.

Experimental feline panleucopenia in the conventional cat.

Coventional kittens, 12-27 weeks old, were inoculated with cell-cultured feline panleucopenia virus and killed sequentially between day 3 and day 24 after inoculation. All developed a non-fatal mild disease between days 2 and 9, characterized by lymphopenia, neutropenia, listlessness, depression and the development of neutralizing antibodies to the virus. Small intestinal bacterial counts were reduced during the period of maximal clinical disease, presumably a result of decreased food intake. There was involution of the thymus with marked depletion of lymphocytes between days 3 and 12. Depletion of lymphocytes also characterized the lesions in the lymph nodes between days 3 and 8. At the same time crypt lesions with spotty distribution were in the small intestinal and colonic mucosa. The changes were loss of crypt epithelial cells with compensatory attenuation of the remaining epithelium. Electron microscopically, the number and size of microvilli and secretory granules were reduced but there was no change indicating lethal cell injury. There were no virus particles. The findings point to an early and transient cellular damage by the virus. Intestinal alkaline phosphatase activity disappeared from the luminal surface of the attenuated crypt epithelial cells. Otherwise, intestinal alkaline and acid phosphatase activity were not altered in inoculated cats.

The formation of the gonadal ridge in Xenopus laevis: I. A light and transmission electron microscope study

ABSTRACT In Xenopus laevis tadpoles, between stages 44 and 49 (Nieuwkoop &amp; Faber, 1956), the primordial germ cells (PGCs) migrate from the dorsal mesentery of the gut to the site of the presumptive gonadal ridge. This paper describes the process at the light- and electronmicroscope levels. The PGCs in the mesentery, which at first are very large and yolk-laden, seem to lie entirely within the cellular matrix of the mesentery, although this is not obvious in light micrographs. Where the PGCs bulge out into the coelomic cavity, they stretch the somatic cell covering to a thin, cytoplasmic layer. The somatic cells of the mesentery are held together around them at this stage by well-differentiated desmosomes. At this, and subsequent stages, the PGCs have cytoplasmic processes, roughly the size of microvilli, which are irregularly distributed over their surfaces, and which are inserted between surrounding somatic cells. Whether these processes play any role in locomotion or exploration of the substrate is uncertain. As the PGCs move laterally from the root of the mesentery to the presumptive gonadal ridge, the coelomic lining cells which cover them, initially with a very thin squamous layer, differentiate to form the cuboidal cells of the germinal epithelium. Several interesting ultrastructural features of these cells, and the PGCs, are described, particularly in the light of their surface interaction. In the light of the morphological data presented here, particularly of the cell surfaces involved, we conclude that both active locomotion by the PGCs and passive movement by the morphogenetic movements of the cells around them contribute to the establishment of the early gonadal ridge.

Differentiation and degeneration of crayfish photoreceptors in darkness.

Photoreceptor cells of the compound eye were studied electron microscopically in crayfish Procambarus clarki that had been grown in complete darkness for 11 weeks. Since the microvilli of recently differentiated retinula cells appeared uniform in size and were regularly oriented, light is not necessary for their development. Variability in size of microvilli due to enlargement and disruption of their normal orientation became progressively greater with the age of the cell, therefore, light is needed for maintenance of normal features and apparently of function. Behavioral experiments with 2 older light-deprived animals indicated that they were blind.