An examination of surface epithelium structures of the embryo across the genus Poeciliopsis (Poeciliidae)

In viviparous, teleost fish, with postfertilization maternal nutrient provisioning, embryonic structures that facilitate maternal‐fetal nutrient transfer are predicted to be present. For the family Poeciliidae, only a handful of morphological studies have explored these embryonic specializations. Here, we present a comparative morphological study in the viviparous poeciliid genus, Poeciliopsis . Using microscopy techniques, we examine the embryonic surface epidermis of Poeciliopsis species that vary in their level of postfertilization maternal nutrient provisioning and placentation across two phylogenetic clades and three independent evolutionary origins of placentation. We focus on surface features of the embryo that may facilitate maternal‐fetal nutrient transfer. Specifically, we studied cell apical‐surface morphology associated with the superficial epithelium that covers the body and sac (yolk and pericardial) of embryos at different developmental stages. Scanning electron microscopy revealed common surface epithelial cells across species, including pavement cells with apical‐surface microridges or microvilli and presumed ionocytes and/or mucus‐secreting cells. For three species, in the mid‐stage embryos, the surface of the body and sac were covered in microvillus epithelium. The remaining species did not display microvillus epithelium at any of the stages examined. Instead, their epithelium of the body and sac were composed of cells with apical‐surface microridges. For all species, in the late stage embryos, the surface of the body proper was composed of apical‐surface microridges in a “fingerprint‐like arrangement.” Despite the differences in the surface epithelium of embryos across Poeciliopsis species and embryonic developmental stages, this variation was not associated with the level of postfertilization maternal nutrient provisioning. We discuss these results in light of previous morphological studies of matrotrophic, teleost fish, phylogenetic relationships of Poeciliopsis species, and our earlier comparative microscopy work on the maternal tissue of the Poeciliopsis placenta.     

Light and electron microscopic studies on the pars intermedia of the chameleon

Summary The neurointermediate lobe of the hypophysis in the Chameleon (Chamaeleo dilepis) was examined with light and electron microscopic methods, with special reference to the cytology of the pars intermedia (PI). The PI is the largest lobe of the hypophysis consisting of (1) dark cells with secretory granules ranging from 200–600 nm; (2) light cells, far fewer in number, containing granules 150–300 nm in diameter; (3) stellate, non-secretory cells. The secretory cells abut onto the perivascular basal lamina of the capillary sinusoids while their apical part borders an intercellular space. This surface of the cells often bears a cilium. The granules arise from the Golgi cisternae while small detached vesicles are found between circumscribed sites of the cell membrane and the Golgi apparatus. No nervous elements were found in the pars intermedia and it is assumed that the regulation of this lobe is purely humoral. This is supported by the presence of three types of nerve terminals in the pars nervosa: (a) terminals with large secretory granules and small vesicles; (b) terminals with dense-core vesicles and small vesicles; (c) terminals with small vesicles only. All of these are secretory as indicated by the presence of the synaptic semidesmosomes formed with the perivascular basal lamina.I would like to thank Mr. W.N. Newton for his skill and aid in all aspects of this work, Mr. A. Ansary for expert photographic assistance and the Central Pathology Laboratory, University of Dar es Salaam, for the electron microscopic facilities provided. Research sponsored by the University of Zambia Grants J02-18-00 and Medic 74/6     

Trans-epidermal Transport and Storage of Calcium in Holthuisana transversa (Brachyura; Sundathelphusidae) During Premoult

Holthuisana transversa reabsorbs much of its exoskeletal calcium in the last 3 days before ecdysis and stores it in circulating granules in the haemocoel and in non-circulating granules in the subepidermal connective tissue. Calcium enters the epidermal cells from the moulting fluid, probably through their apical microvilli and is either incorporated into intracellular calcium granules or exits the cell via the basolateral membranes to be used in formation of two other granule types. Intracellular granules (0.4–2 μm long) form in large masses in the apical cytoplasm of the epidermal cells. They are formed as membrane-bound vesicles by the Golgi, and calcium and organic matrix material are added from the surrounding cytoplasm. As development proceeds, lamellae appear and calcium carbonate is deposited in the matrix. Granule masses move basally and are stored in the connective tissue. Calcium is also incorporated into extracellular large granules (0.8–3.8 μm long) which are formed in narrow intercellular channels between epidermal cells. A third granule type (small granules, 0.26 μm diameter) is formed in subepidermal connective tissue cells and released into the haemolymph in very large numbers. Calcium was identified in the two larger granule types using X-ray microanalysis and significant amounts of phosphorus and potassium were also present in the large granules. A model for ion cycling between the exoskeleton and granules is presented.     

The Golgi apparatus in epidermal mucoid and ellipsoid-vacuolate cells ofAeolidia papillosa andCoryphella rufibranchialis (Nudibranchia)

Summary The epidermal cell layer of the apical end of the ceras was investigated in two species of aeolid nudibranchs. Based on cellular inclusions, mostly two cell types were found: mucoid and ellipsoid-vacuolate cells. Mucoid cells ofCoryphella rufibranchialis have large heterogeneous and fibrillar secretory granules whereas inAeolidia papillosa, the granules are homogeneous, but vary in electron density from one cell to another. Ellipsoid-vacuolate cells contained large quantities of small vacuoles with an included ellipsoidal structure. Both species contained very numerous ellipsoid-vacuolate cells. Secretory granules and ellipsoid-vacuoles appear to arise from the Golgi apparatus and these contents stain with PAS, suggesting a polysaccharide composition. Mucoid cells contained both secretory granules and ellipsoid-vacuoles which may arise from the same Golgi apparatus.     

Observations on the anterior testicular ducts in snakes with emphasis on sea snakes and ultrastructure in the yellow‐bellied sea snake,Pelamis platurus

The anterior testicular ducts of squamates transport sperm from the seminiferous tubules to the ductus deferens. These ducts consist of the rete testis, ductuli efferentes, and ductus epididymis. Many histological and a few ultrastructural studies of the squamate reproductive tract exist, but none concern the Hydrophiidae, the sea snakes and sea kraits. In this study, we describe the anterior testicular ducts of six species of hydrophiid snakes as well as representatives from the Elapidae, Homolapsidae, Leptotyphlopidae, and Uropeltidae. In addition, we examine the ultrastructure of these ducts in the yellow‐bellied Sea Snake, Pelamis platurus, only the third such study on snakes. The anterior testicular ducts are similar in histology in all species examined. The rete testis is simple squamous or cuboidal epithelium and transports sperm from the seminiferous tubules to the ductuli efferentes in the extratesticular epididymal sheath. The ductuli efferentes are branched, convoluted tubules composed of simple cuboidal, ciliated epithelium, and many species possess periodic acid‐Schiff+ granules in the cytoplasm. The ductus epididymis at the light microscopy level appears composed of pseudostratified columnar epithelium. At the ultrastructural level, the rete testis and ductuli efferentes of P. platurus possess numerous small coated vesicles and lack secretory vacuoles. Apocrine blebs in the ductuli efferentes, however, indicate secretory activity, possibly by a constitutive pathway. Ultrastructure reveals three types of cells in the ductus epididymis of P. platurus: columnar principal cells, squamous basal cells, and mitochondria‐rich apical cells. This is the first report of apical cells in a snake. In addition, occasional principal cells possess a single cilium, which has not been reported in reptiles previously but is known in some birds. Finally, the ductus epididymis of P. platurus differs from other snakes that have been studied in possession of apical, biphasic secretory vacuoles. All of the proximal ducts are characterized by widening of adjacent plasma membranes into wide intercellular spaces, especially between the principal cells of the ductus epididymis. Our results contribute to a larger, collaborative study of the evolution of the squamate reproductive tract and to the potential for utilizing cellular characters in future phylogenetic inferences. J. Morphol. 2012. © 2011 Wiley Periodicals, Inc.     

Ultrastructure of the vasa deferentia of the mediterranean flour moth

Each vas deferens of the Mediterranean flour moth, Anagasta kuehniella (Zeller), consists of a short swollen portion immediately below the testis, another swollen portion that forms a seminal vesicle, and an elongate lower portion that empties into one arm of the ductus ejaculatoris duplex. Three types of epithelial cells occur sequentially. Phagocytic cells that engulf debris from the testis form the anterior two-thirds of the first swollen portion. Tall secretory cells form the distal third of the first swollen region and extend to the seminal vesicles. The secretory cells surround a slit-like lumen and appear to function as a valve between the two swollen regions. Many membrane-enclosed secretory granules are stored at the apical ends of the cells and are released into the lumen together with small amounts of the surrounding cytoplasm. The granules remain intact while they are in the male tract. A second type of secretory cell forms the walls of the seminal vesicles and the lower vasa deferentia. These cells produce secretory granules whose contents become dispersed through the semen. PTA-chromic acid staining indicates that the seminal plasma has a high glycoprotein content. A thin muscle layer is basal to the epithelial cells. Both apyrene and eupyrene sperm undergo some development in the vasa deferentia. The epithelial cells, muscle, and stored sperm all undergo extensive changes with age.     

Histological development of the cement gland in Xenopus laevis: a light microscopic study

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

Testis differentiation in the glowworm, Lampyris noctiluca, with special reference to the apical tissue.

The gonads of Lampyris noctiluca are sexually undifferentiated during the first larval instars. They consist of many gonadal follicles that include the germ stem cells enclosed by the somatic cells of the follicle wall. Follicle wall cells are more numerous at the follicle apices than at the distal parts, but different cell types cannot be distinguished. In male larvae, the appearance of apical follicle tissue, derived from follicle wall cells, marks the onset of testis differentiation. When maximally expressed, the apical tissue occupies about the upper half of the testis follicles and can be observed in larvae of the fifth and sixth instar. The apical tissue is characterized by its "light" appearance (due to poor stainability) caused by the small number cellular organelles, especially a paucity of free ribosomes. Maximal expression of the apical tissue must be very brief, since in most examined fifth and sixth instar larvae the apical tissue is partly or mostly translocated into the center of the upper half of the follicles and spermatogonia then occupy the apical follicle tips. During and after translocation apical cells form projections that grow around clusters of spermatogonia (spermatocysts). Thus, the apical cells transform into spermatocyst envelope cells. They retain their "light" appearance but undergo dramatic subcellular differentiation: smooth ER becomes extremely prominent, forming stacks and whorls of parallel cisternae. Golgi complexes are also conspicuous. The cellular organization suggests secretory activity. The possibility of ecdysteroid production and its function is discussed. The spermatocyst envelope cells persist into the pupal stage. When spermiohistogenesis takes place in cysts, cyst envelope cells show signs of regression. At all stages of testis development apical cells and their derivatives, the spermatocyst envelope cells, phagocytize degenerating spermatogonia. Although this is an important task of these cells, the impressive formation of sER in the cyst envelope cells is indicative of an additional, as yet unknown, function.     

A morphologic study of the ductus of the epididymis of Sus domesticus

The head, body, and tail regions of the epididymal duct (or caput, corpus, and cauda epididymis) in two healthy and sexually mature Sus domesticus males were examined by light microscopy and by scanning or transmission electron microscopy. The epididymal duct is lined with a pseudostratified epithelium with stereocilia and covered by a muscular-connective tissue sheath that is thickest in the tail region. Diameter of the epididymal duct and height of epididymal epithelium are maximal in the head region. Length of the sterocilia and spermatic density are higher in the head and body regions. Somatic cells are abundant in the tail region. The epididymal epithelium is made up of five cell types: basal cells, principal cells, clear cells, narrow cells, and basophilic cells. Abundant secretory units are observed in the supranuclear cytoplasm of columnar principal cells. Each mature secretory unit is constituted by electron-dense secretion granules covered by more than eight layers of cisternae of reticulum between which the mitochondria are intercalated. In the apical cytoplasm the isolated secretion granules become larger and less electron dense. The apical surface is covered by numerous sterocilia. Basal cells are pyramidal and less high than principal cells. The clear cells, arranged between the principal cells, are characterized by the presence of abundant vesicular elements and electron-lucid secretion granules, and by an apocrine secretory process. The narrow cells are characterized by their highly vacuolized cytoplasm. Intermediate cell typologies can be found among basal, principal, clear, and narrow cells, which could be four developmental stages of the same cell type. The basophilic cells are spheroidal and are found at different levels between the epithelial cells and in the connective tissue underlying the epithelium. © 1993 Wiley-Liss, Inc.     

A light and electron microscopic study of myelopoietic cells in the perihepatic subcapsular region of the liver in the adult aquatic newt,Notophthalmus viridescens

Summary The liver of the newt, Notophthalmus viridescens, consists of several incompletely separated lobes of parenchymal tissue each of which is covered by a perihepatic subcapsular region (PSR) of myeloid tissue. This tissue contains neutrophils and eosinophils in various stages of differentiation. As neutrophils develop from myeloblasts to late neutrophilic myelocytes, two types of granules appear. The primary granules (type of granules formed first) are more electron dense and smaller than the secondary granules (type of granules formed later). The primary granules first appear at the stage designated early neutrophilic myelocyte, and the secondary granules appear at the stage of the maturing neutrophilic myelocyte. The eosinophils present are characterized by much larger granules than those observed in neutrophils. Cells in the PSR which superficially resemble small lymphocytes are primitive stem cells that give rise to neutrophils and eosinophils. The liver PSR is invested by a visceral peritoneum of simple squamous mesothelial cells some of which are ciliated.Supported by ACS IN-105.     

Ultrastructural study of the retinal pigment epithelium during metamorphosis in the sea lamprey (Petromyzon marinus L.)

Summary The sequence of morphological changes in the retinal pigment epithelium during the metamorphic period of the sea lamprey Petromyzon marinus L. has been investigated using electron microscopy. At early metamorphic stages (stages I and II), photoreceptors are present in a small zone of the retina. During these stages, the lateral surface of the epithelial cells shows zonulae occludentes and adhaerentes. The degree of cell differentiation varies throughout the retinal pigment epithelium. Cells covering the differentiated photoreceptors in the central retina have phagosomes, whereas pigment granules appear only in the retinal pigment epithelium dorsal to the optic nerve head. Most epithelial cells have myeloid bodies; their morphology is more complex around the optic nerve head. At stage III, when photoreceptors develop over the whole retina, the distribution of cytoplasmic organelles is almost homogeneous in the retinal pigment epithelium. Subsequently, the basal plasma membrane of the epithelial cells becomes progressively folded and their apical processes enlarged. In addition, extensive gap junctions develop between retinal pigment cells. In late metamorphic stages, noticeable growth of myeloid bodies occurs and consequently the retinal pigment epithelium resembles that of the adult. This study also describes, for the first time, the presence of wandering phagocytes in the retinal pigment epithelium of lampreys; their role in melanosome degradation is discussed.     

Comparative ultrastructure of Langerhans‐like cells in spleens of ray‐finned fishes (Actinopterygii)

We studied the morphology and occurrence of splenic Langerhans‐like (LL) cells in species representing 11 orders of ray‐finned fishes, Actinopterygii. LL cells were frequent in spleen tissue of species among Cypriniformes, Esociformes, Salmoniformes, and Pleuronectiformes. These cells contained granules which resembled Birbeck granules known to occur in mammalian Langerhans cells. The ultrastructure of LL cells in Northern pike, Esox lucius, and in Atlantic halibut, Hippoglossus hippoglossus were similar to those reported in salmonids. LL cells found in cyprinids shared some characteristics with the LL cells in other Actinopterygii species, although unique structures distinguished them from the latter. They contained dense bodies within the Birbeck‐like (BL) granules, a characteristic that was never observed in species outside the Cypriniformes. Two types of BL granules were characterized in cyprinid LL cells. The ultrastructure of BL granules across the species is discussed. LL cells in all Actinopterygii species demonstrated close contacts with nearby cells, characterized by adherens‐like junctions. Additionally, multivesicular bodies were present within the cytoplasm and large aggregates of exosomes were observed closely associated with the plasma membrane suggesting their release from the cells. These structures are discussed in relation to mammalian dendritic cells. Macrophages found in European perch, Perca fluviatilis, blue gourami, Trichogaster trichopterus, and Atlantic halibut, Hippoglossus hippoglossus contained lysosomes and residual bodies with structures resembling Birbeck granules. These granules and cells were clearly distinct from LL cells. J. Morphol. 2010. © 2010 Wiley‐Liss, Inc.     

Ultrastructure of endocrine cells in the stomach of two teleost fish Perca fluviatilis L. and Ameiurus nebulosus L.

Summary In the gastric mucosa of two teleost species, the perch (Perca fluviatilis) and the catfish (Ameiurus nebulosus) three endocrine cell types were found, located predominantly between the mucoid cells of the gastric mucosa. A fourth cell type is present in the gastric glands of catfish. Each cell type was defined by its characteristic secretory granules. Type-I cells were predominant in both fish. These cells contained round or oval granules with a pleomorphic core. The average diameter of granules was 400 nm for the perch and 270 nm for the catfish. Type-II cells of both species displayed small, highly osmiophilic granules about 100 nm in diameter. The secretory granules of type-III cells (260 nm in the perch and 190 nm in the catfish) were round or slightly oval in shape and were filled with a finely particulate electron-dense material. Type-IV cells of the catfish were found in the gastric glands only. Their cytoplasm was filled with homogeneous, moderately electron-dense granules averaging 340 nm in diameter. The physiological significance of these different morphological types of gastric endocrine cells requires further investigation.     

Iodine metabolism of the endostyle of larval lampreys,ammocoetes of Lampetra japonica

Summary Experiments were carried out to study the iodine metabolism of the endostyle of the larval lamprey which is considered to be homologous to the thyroid gland. Larval lampreys, ammocoetes of Lampetra japonica were intraperitoneally injected with 200 c of Na ¹²⁵I; their endostyles were removed 30 minutes, 1, 2, 4, 6, 8 and 24 hours after the treatment. Type 1 and type 4 cells (Marine) were almost inactive in binding iodine. Silver grains appeared within 30 minutes after the injection over the apical cell membrane including the surfaces of microvilli and cilia of type 2 c and type 3 cells. These grains increased in number until 2 hours. A few of apical small vesicles of the same cells were labeled 1 to 2 hours after the injection. Small dense granules large dense bodies, and multivesicular bodies in the type 2 c and type 3 cells were labeled especially at 6 to 24 hours. The ratio in number of the labeled dense granules, or bodies to the unlabeled ones tended to increase markedly with time. Large or small vacuoles, dense or light in the cytoplasm of some type 5 cells which lack indications of protein-synthesis sign in the cytoplasm were labeled 6 to 24 hours after the injection of ¹²⁵I, and the number of the labeled vacuoles increased with time. From these facts, we conclude that: (1) iodination of the thyroglobulin of type 2c and type 3 cells takes place almost entirely at the apical cell membrane region, (2) the thyroglobulin-like protein contained in the apical small vesicles of type 2c and type 3 cells is slightly iodinated, (3) although it is difficult to determine whether the dense granules and bodies, which might be lysosomes, are secretory substances or reabsorbed materials, the possibility of the occurrence of reabsorption and hydrolysis of the thyroglobulin in the type 2c and type 3 cells should be considered, and (4) reabsorption of the thyroglobulin from the endostylar lumen by some type 5 cells should be also considered.     

Cellular succession in the epithelium lining the pharyngeal cavity of planarians

Regardin cell renewal of planarian epithelial tissue, little is known at present except for the epidermis (Tyler, 1984). According to Skaer (1965), the definitive epidermal cells in planarian embryos originate in the parenchyma where they develop as precursor cells which then migrate into the epidermis. This process of development is also reported in regenerating planarians (Spiegelman & Dudley, 1973; Morita & Best, 1974; Hori, 1978). Recently the validity of Skaer's conclusion has clearly been confirmed by Ishii & Sakurai (1998) using SEM and TEM.The present study deals with the origin and renewal of cells of another epithelium — that lining the pharyngeal cavity of a freshwater planarian Dugesia japonica. This epithelium is known to consist of cells with secretory granduls of fingerprint-like structure (Ishii, 1966; Bowen & Ryder, 1973; Gamo & Garcia-Corrales, 1988; Asai, 1991). The characteristic feature of these specific granules, as well as epitheliosomes (Tyler, 1984) of the epidermis, is very useful as a cell marker for distinguishing cell types and following cell differentiation. Gamo & Garcia-Corrales (1988) claimed the cell populations of the pharyngeal epithelium of Dugesia gonocephala is morphologically and functionally heterogeneous. The sequence of morphological alteration offers the oppurtunity to distinguish at least three functional stages. These represent different adaptive forms of a single cell type, and indicate transformation from one to the next induced by cell renewal. It suggests a beta cell (noeblast) origin of the epithelial cells.In the present study SEM observations revealed theat there are morphologically three distinct cell types which are considered to be juvenile, mature, and senile cells respectively, judging from the differences in cells and the many transitional forms among them (Fig. 1). When observed by TEM, the cytoplasmic patterns of these cell types are correspondingly different from one another, similarly the surface specializations of the plasma membranes of each cell type which facilitate their identification by TEM also vary. Apparently alterations of cell morphology are involved in ageing in a single cell type. Morphological features of each cell type are summarized. Juveniles (R) rarely occur, are small cells provided with prominent apical ruffles and considered to be phagocytic because the cells often contain newly formed phagosomes. Mature cells (F) predominate, are large, polygonal, flat cells, presumably with an intense secretory activity. The cells contain many profiles of granular ER and a small number of specific (secretory) granules. Senile cells (M) are intermittently distributed, irregularly contoured cells with heavy surface microvilli. The specific granules are dense in the apical cytoplasm, and profiles of granular ER decease in number.The precursor epithial cells that are seen in the parenchyma exhibit a considerable degree of differentiation before their translocation into the lining. The primordial cells observed are neoblast-like, with several cohromatoid bodies and many free ribosomes (Morita et al., 1969). These results obtain thus support the evidence and prediction of Gamo & Garcia-Corrales (1988). The observed mode of cell replacement appears to be the same as found in the epidermis (Lentz, 1967).     

Subcellular distribution of tissue kallikrein and Na,K-ATPase α-subunit in rat parotid striated duct cells

Intracellular protein distribution and sorting were examined in rat parotid striated duct cells, in which tissue kallikrein is apical, and Na,K-ATPase is basolateral. Electron-microscopic immunogold cytochemistry, with both polyclonal and monoclonal antibodies, demonstrated these enzymes at opposite poles of the cells and in distinct intracellular sites. Kallikrein was found within apical secretory granules, whereas Na,K-ATPase was present on basolateral cell membranes. In addition, kallikrein was localized throughout cisternae of all Golgi profiles, whereas Na,K-ATPase (-subunit) was found only in small peripheral vesicles and/or lateral cisternal extensions of a basal subset of Golgi profiles. These differences in the subcellular distribution of the two marker antigens were most clearly seen with double immunogold labelling. Our results suggest that kallikrein, an apical, regulated secretory protein, and Na,K-ATPase, a basolateral, constitutively transported membrane protein, are segregated at (or prior to) the level of the Golgi apparatus rather than in the trans-Golgi network (TGN), as was expected.Abbreviations ATP adenosine tri-phosphate - HBSS Hanks' balanced salt solution - GaM goat anti-mouse - GaR goat anti-rabbit - PBS phosphate-buffered saline - RaM rabbit anti-mouse - RER rough endoplasmic reticulum - TGN trans-Golgi network     

Organization of interstitial tissue in the testis of the salamander Necturus maculosus (Caudata: Proteidae)

In Necturus maculosus the organization of the interstitial tissue varies according to the stage of spermatogenesis. Leydig cells at various stages of differentiation and myoid cells are always present in this tissue. The Leydig cells are undifferentiated at all phases of germ cell activity and only hypertrophy following spermiation and degeneration of Sertoli cells. These Leydig cells are structurally analogous to mammalian Leydig cells. They do not form part of the lamina propria of the seminiferous lobules and hence cannot be referred to as lobule-boundary cells previously described in the urodele testis (Lofts, '74). When the Leydig cells hypertrophy, numerous unmyelinated axons appear in the interstitial tissue. These axons, often devoid of Schwann-cell cytoplasm, occur in close proximity to Leydig cells. Because the levels of both Substance P and neurotensin increased in the testis of Necturus maculosus as Leydig cells differentiated, we concluded that these neural elements may regulate Leydig-cell function locally, through the release of neuropeptides.     

Ultrastructure of the sexual segments of the kidney in male and female lizards,Cnemidophorus l. lemniscatus (L.)

Summary Kidneys of adult male and female lizards were studied by electron microscopy, in order to understand the ultrastructure of the collecting duct and a differentiated part thereof, the sexual segment, which is an important accessory sexual organ. First portion of sexual segment in males: The cells are filled with large secretory granules of a wide range of opacities. The granular endoplasmic reticulum is abundant; basal formations of superimposed flat cisternae are frequent. Distended vesicles and microvesicles prevail in the supranuclear, well developed Golgi apparatus. Evidences indicate that secretion of these cells is holocrine. Second portion of sexual segment in males: All of the secretory granules are apical in location and relatively electron-opaque; they show a denser core. This core is formed by a substance which, after lying in contact with ribosomes, enters the secretory vesicles of the highly developed Golgi apparatus. A lighter substance is then condensed around it. The secretion of the granules is merocrine. The granular endoplasmic reticulum is very abundant in these cells, but basal ergastoplasmic formations are lacking. Sexual segment in females: The cells show features similar to those of the male first portion, but they are smaller. Undifferentiated collecting duct: Most of the cells are mucigenic. They have small ovoid, apical secretory granules. The density of the granules varies from cell to cell; when they are electron-lucent, they exhibit laminar or dotted opaque figures. Moderately developed Golgi apparatus and granular endoplasmic reticulum, as well as elongated mitochondria, occur in mucigenic cells. Intercalated among the latter are non-secretory cells. They have very abundant mitochondria, numerous microvilli, many pinocytic and smooth-membrane vesicles, whereas the organelles participating in synthetic processes are poorly developed; their function is most likely related to active solute transport.     

Hemocytes of the palaemonids Macrobrachium rosenbergiiand M. acanthurus,and of the Penaeid Penaeus paulensis

The hemocytes of two palaemonids and one penaeid were characterized using light and transmission electron microscopy (TEM). The blood cells in all three species were classified as hyaline hemocytes (HH), small granule hemocytes (SGH), and large granule hemocytes (LGH). The HH are unstable hemocytes with a characteristic high nucleo-cytoplasmic ratio. Their cytoplasm appears particularly dense and has from few to numerous granules that often exhibit a typical striated substructure. In both palaemonids, the great majority of the HH contain numerous granules, whereas in Penaeus paulensis, a small number of these cells have few or no granules. The cytoplasm of some HH of the penaeid exhibits typical electron-dense deposits. The granulocytes, LGH and SGH, contain abundant electron-dense granules that are usually smaller in the SGH. In both hemocyte types, the cytosol, but not the granules, is rich in carbohydrates (PAS positive) and numerous vesicles contain acid phosphatase (Gomori reactive). In all studied shrimps, the SGH and LGH were actively phagocytic when examined on blood cell monolayers incubated with the yeast Saccharomyces cerevisiae. A few mitotic figures (less than 1%) were observed in the granulocytes of P. paulensis, but not in the palaemonids. SGH is the main circulating blood cell type in both palaemonids, whereas HH is predominant in the penaeid. Based on morphological and functional features, it appears that the hyaline and the granular hemocytes of the three shrimp species represent different cell lineages. J. Morphol. 236:209–221, 1998. © 1998 Wiley-Liss, Inc.