Thin section and freeze fracture studies of the hypophyseal proximal pars distalis in a teleost (Rhamdia hilarii Val.) during different stages of the reproductive cycle

Summary Chromophilic cells in the proximal pars distalis of the adenohypophysis of Rhamdia hilarii were studied in thin section and freeze fracture preparations. The gonadotropic cells (GTH-cells) exhibit a diversity of form, the frequency of which can be related to stages (maturation, mature and spent) in the sexual cycle. GTH-cells showing a cytoplasm filled with electron dense polymorphic secretory granules and small rough endoplasmic reticulum (RER) vesicles, have been termed non-vacuolated. During the mature gonadal stage, such cells become increasingly vacuolated. The small RER vesicles become dilated and/or fuse, forming a single enormous cisternum (4–11 m diameter), the contents of which show direct contact with the inner nuclear membrane. These morphological aspects support the idea that Rhamdia hilarii possesses only one GTH-cell type. Evidence from freeze fracture replicas suggests that membrane-associated events precursory to exocytosis take place in regions where the cell and secretory granule membranes are in close apposition. Thin section analysis of secretory granule formation revealed their derivation from the dilated extremities of the inner Golgi saccule which appears to resemble the rigid lamella described in other cells. After detachment of the inner saccule, the immature secretory granules appear to enlarge by microvesicular transport. Freeze fracture and ultrastructural data on the morphology of the cells that presumably synthetise growth hormone are also presented.This work was aided by the Fundação de Amparo à Pesquisa do Estado de São Paulo (75/1282)     

The brain-pituitary-gonadal axis in the rainbow trout,Salmo gairdneri: Gonadal hormones and the maturation of gonadotropic cells

Summary Intact and castrated juvenile male rainbow trout (Salmo gairdneri) were treated with testosterone and gonadotropic hormone (GTH) to determine the maturational effects of these hormones on the GTH-cells. Electron-microscopic studies of the GTH-cells revealed that GTH and testosterone in intact animals, and testosterone in castrated fish, caused GTH-cell maturation: These cells now displayed the same appearance as GTH-cells in adult trout, including the presence of globules, a well-developed Golgi apparatus and rough endoplasmic reticulum, all of which were absent in GTH-cells of control animals. Animals with stimulated GTH-cells also had an increased GTH content of the pituitary; release of GTH could not be demonstrated. Animals treated with GTH exhibited an accelerated development of the testes, resulting in complete gametogenesis and elevated plasma testosterone levels. These results indicate that exogenous steroids as well as endogenous gonadal steroids can stimulate the full development of GTH-cells and accelerate GTH synthesis. The significance of this stimulating effect of the gonadal hormones with respect to the development of the brain-pituitary-gonadal axis and the onset of puberty is discussed.The results were presented as a poster at the 11th conference of the European Society of Comparative Endocrinology, Jerusalem, August 10–14, 1981     

Dynamic changes in insoluble polysaccharides and neutral lipids in the developing anthers of an endangered plant species, <Emphasis Type="Italic">Pancratium maritimum</Emphasis>

Dynamic changes in the distribution of lipid and insoluble polysaccharide reserves of Pancratium maritimum L. (Amaryllidaceae) anthers were investigated throughout the successive stages of pollen development, using cytochemical methods, to determine whether the synthesis, transformation, and mobilization of reserve materials in developing anthers follow the regular pathway in angiosperms and support the physiological activities in developing pollen. Polysaccharides and lipid reserves exhibited a variable pattern of distribution from the sporogenous cell stage to the anthesis. Starch granules and lipid bodies were scarce in the cytoplasm of sporogenous cells, but their number increased significantly at the premeiotic stage. Conversely, starch and lipid reserves of meiocytes reduced at the early prophase of the first meiotic division, and then their amount showed fluctuations during the microsporogenesis. The cytoplasm of free and vacuolated microspores was poor regarding the polysaccharide and lipid reserves. However, at the late vacuolated microspore stage, small insoluble polysaccharides began to appear in the microspore cytoplasm, and their number increased remarkably in the cytoplasm of the bicellular pollen grain. During the maturation of pollen grains, polysaccharide reserves were replaced with lipids. The starch and lipid reserves of the staminal envelope also showed variations at different stages of the anther development. The dynamic changes in the polysaccharide and lipid reserves of P. maritimum anthers were consistent with the physiological activities such as differentiation, cell division and material synthesis that occur in the anther tissue at different stages of the male gametophyte development, and supported the normal pollen development.     

Somatic embryogenesis from seed explants of Abies alba

Megagametophytes of Abies alba containing the immature embryos were dissected from the seed coats and divided by longitudinal and transverse sections. They were placed with the cut surface down on modified Schenk & Hildebrandt medium containing 50 mgl^-1 myo-inositol and 2% sucrose, supplemented with 1 mgl^-1 N⁶-benzyladenine (BAP). An embryogenic type of callus proliferated after one month of culture. Closer examination revealed the presence of structures resembling early stages of embryogenesis as well as of single elongated, vacuolated cells and clusters of cells with dense cytoplasm. Under appropriate conditions, some of the somatic embryos elongated and formed cotyledons.     

Late steps of egg cell differentiation are accelerated by pollination in Zea mays L.

 Egg cells were analysed cytologically during the female receptivity period in maize (Zea mays L., line A 188). Three classes of egg cell were distinguished: type A – small, non-vacuolated cells with a central nucleus; type B – larger cells with small vacuoles surrounding the perinuclear cytoplasm located in the middle of the cell; type C – big cells with a large apical vacuole and the mid-basal perinuclear cytoplasm. The less-dense cytoplasm of the vacuolated egg cells usually contained numerous cup- or bell-shaped mitochondria. The three egg types appear to correspond to three late stages of egg cell differentiation. The frequencies of each of the three egg types were monitored in developing maize ears before and after pollination. In young ears, with the silks just extending out of the husks, small A-type cells were found in about 86% of ovules. Their frequency decreased to about 58% at the optimum silk length, remained unchanged in non-pollinated ears, and fell to 16% at the end of the female receptivity period. However, after pollination and before fertilisation the frequency of these cells decreased to about 33%, and the larger vacuolated egg cells (types B and C) prevailed. At various stages of the receptivity period, pollination accelerated changes in the egg population, increasing the number of ovules bearing larger, vacuolated egg cells. Experiments with silk removal demonstrated that putative pollination signals act immediately after pollen deposition and are not species-specific. Received: 5 February 1999 / Accepted: 28 August 1999     

Ultrastructural localization of calcium and Ca2+-ATPase activity in gonadotrops and stellate cells of the catfish pituitary

Summary In the pituitary of the African catfish, Clarias gariepinus, calcium precipitates were ultrastructurally visualized with the oxalate-pyroantimonate procedure (OPP). The presence of calcium in these precipiates was validated with several methods, including Electron Energy Loss Spectrometry (EELS). In the OPP-treated tissue calcium precipitates were seen in a) non-secretory stellate cells and b) gonadotropic (GTH-) cells. In the latter the amount of precipitate is generally low, but stimulation of the gonadotropin release, either in vivo or in vitro, resulted in a considerable increase. This increase is discussed in relation to the role of calcium as second messenger in the GTH-cells. Ca²⁺-ATPase was exclusively represented in stellate cells and GTH-cells, its strongest activity associated with the plasma membrane and with the membranes of the endoplasmic reticulum. The localization of this enzyme is discussed in relation to its role in the regulation of the intracellular calcium concentration in the GTH-cells. The stellate cells are considered to be involved in the regulation of extracellular calcium concentrations in the pituitary.     

Fetal erythropoiesis in steel mutant mice : I. A morphological study of erythroid cell development in fetal liver

A method of definitive identification of mutant (S1/S1^d) and wild-type (+/+) mouse embryos in segregating litters is described, based on the total number of circulating erythrocytes in a unit volume of embryonic blood and the relative proportion of nonnucleated vs. nucleated red blood cells. Evidence is presented that from days 13–17 of gestation, S1/S1^d embryos have many fewer fetal liver derived nonnucleated erythrocytes whereas the number of yolk sac-derived nucleated red blood cells is similar between S1/S1^d and +/+. Erythroid precursor cells at various stages of maturation in mutant fetal livers are studied by light and electron microscopy, and their fine structure is found to be identical to those present in normal embryos. The number of hemoglobin-containing mature erythroblasts in mutant fetal livers is far fewer than that of the normal, whereas the number of immature erythroid precursors present in a unit area of fetal liver is not significantly different between S1/S1^d and +/+. It is suggested that the mutant S1 gene product(s) interferes with or fails to support the differentiation of immature erythroid precursors into hemoglobin synthesizing cells.     

G2 arrest and differentiation in the petal of Tradescantia clone 4430

The floral organs of Tradescantia clone 4430 were used to investigate, in terms of cell cycle parameters, cellular behaviour during the maturation of a terminally differentiating system. Petals were sampled at different stages of development for (a) cell number; (b) nuclear DNA content by cytophotometry; (c) [³H]thymidine incorporation into nuclei by autoradiography; and (d) pigment production by spectrophotometry. DNA synthesis was confirmed by measurement of [³H]thymidine incorporation into TCA-insoluble material and changes in DNA content by colorimetric estimation of DNA extracts by diphenylamine. The development of the petal involved four sequential steps. First, there was an increase in cell number, an event characterized by mitoses, DNA synthesis, a few cells in G2 and a predominance in G1. Second, there was a cessation of cell division and DNA synthesis when all the cells accumulated in G1. Third, there was a shift of a large proportion of the total cell population from G1 to the G2 stage of the cell cycle and finally, there was pigment production. In addition, cytophotometric analysis of individual tissues in the mature petal revealed tissue specific differences in the proportion of cells in G2.     

Developmental anatomy and ultrastructure of early somatic embryos in European black pine (Pinus nigra Arn.)

Summary Embryogenic callus cultures of European black pine (Pinus nigra Arn.) were established on megagametophytes containing zygotic embryos in early developmental stage. In addition to many elongated cells and disorganized growing clumps they contained early somatic embryos at various stages of development. At all stages of embryogenesis the embryos were organized as bipolar structures. Cell pairs composed of one isodiametric cell with dense cytoplasm and a second large vacuolated cell were the simplest bipolar system. The vacuolated cell underwent senescence. The cytoplasm-rich cell and its derivates divided transversally, resulting in several cytoplasmic cells arranged in row. An early embryonal cylindrical mass was formed by longitudinal division of the cells in a filament. Proximally localized cells in the early embryonal mass became vacuolized and elongated gradually giving rise to the secondary suspensor. Distal cells remained cytoplasmic in character and formed an embryonal mass along the axis of long early somatic embryos. Differences in the proportion of organelles and heterochromatin clumps, thickness of cell walls and number of plasmodesmata between cells at various stages of early somatic embryogenesis were described.     

Pollenkitt formation in Ilex paraguariensis A.St.Hil. (Aquifoliaceae)

 We investigated the cellular and organelle transformations during the formation of the pollenkitt in the secretory tapetum of Ilex paraguariensis. After the dissolution of the callose surrounding the young microspores, the elaioplasts of the tapetum produce many globules of saturated and unsaturated lipids (plastoglobules). Further on, oleosomes with unsaturated lipids, synthesized in the endoplasmic reticulum, accumulate in the tapetal cytoplasm. In contrast to other species, the plastoglobule production seems to precede the oleosome synthesis. The tapetum shows signs of cellular maturation in the late vacuolated microspore stage, when the plastoglobules and oleosomes coalesce and form the pollenkitt mass. In mature stages of the tapetum the pollenkitt is released into the loculus. Finally, it is mainly deposited on the exine, according to the entomophilous character of this species. The mode of pollenkitt formation in Ilex para guariensis and its transfer to the pollen surface is slightly dissimilar to other Angiosperms. Received October 24, 2002; accepted December 2, 2002 Published online: March 20, 2003     

Reproductive cycle and gonadal development of the Atlantic sea urchin Arbacia punctulata in the Gulf of Mexico: changes in nutritive phagocytes in relation to gametogenesis

ABSTRACT

The annual reproductive cycle comprises steady gametogenic activities that synchronize gonadal maturation and spawning rhythms, which are important for aquatic organisms including marine echinoderms (Echinodermata, Echinoidea). In this study, we report the annual reproductive cycle, gonadal development, and changes in nutritive phagocytes (NPs, which accumulate nutrients in germ cells) in relation to gametogenesis of the Atlantic sea urchin (Arbacia punctulata, an edible echinoid) in the Gulf of Mexico. Monthly changes in gonadal development and maturation were observed morphologically and histologically. We calculated gonadosomatic index (GSI) and compared the stages of gonadal development in order to determine the NPs index, and characteristics of germ cells (eggs and sperm) during the annual reproductive cycle. According to GSI and histological analyses, gametogenic activities were classified into four stages of both sexes: mature (June–August), spent (September–November), recovery (December–March), and growing (April–May). The GSI values in both sexes were high during summer months. In males, testicular lobules were densely packed with sperm from June to August. In females, however, mature eggs first appeared in some ovaries in May, numerically increased from June to July, and decreased in August. During gametogenesis, on the other hand, NPs in both testes and ovaries were depleted from June to August. Collectively, our results suggest that the Atlantic sea urchin spawns during summer months in the Gulf of Mexico. This is the first report, to the best of our knowledge, on gonadal development and changes in NPs during the annual reproductive cycle of any Arbacia species in the Gulf of Mexico.     

Flowering and morphological characterization of Dendrocalamus asper androecium and pollen grains

Abstract

Little is known about the reproduction of Dendrocalamus asper because it flowers only every 100 to 120 years. In the present work we describe some reproductive features of this bamboo and characterise flowers and pollen at various developmental stages. Number of pollen grains and ovules per flower, pollen/ovule ratio, in vitro twinning and pollen grain viability in vivo were evaluated and the different stages of floral development identified. Further, we performed a morphological analysis of androecium and pollen development. Seven distinct stages of flower development were identified; four initial stages, a pre-anthetic stage, and two stages of anthetic. Dendrocalamus asper pseudospikelets avoid inbreeding by means of protogyny. The floral and pollen characteristics suggest that the species is anemophilous. The ultrastructural characteristics of free microspores (stage two of floral development), vacuolated microspores (stage five) and mature pollen (anthetic) were analysed. During maturation, pollen grains accumulate larger and more numerous amyloplasts and organelles such as mitochondria. Pollen disperse in the tricellular development stage. Pollen is monoporate with an operculum-like pore, with a rugulate structure and a spinose tectum.     

Response to: Comment on 'Visual cues override olfactory cues in the host-finding process of the monophagous leaf beetle Altica engstroemi'

Intake rates by the Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), of yeast autolysate and sucrose were clearly related to temperature in constant thermal regimes, but consumption occurred only in light. In regimes of fluctuating temperature, rates of consumption were not necessarily related to the temperatures that prevailed during the photophase, but were more consistently related to daily mean temperature and best related to day degrees per day above the gonadotrophic threshold of 13.5 °C. Day degrees per day could be related to age‐specific changes in the daily rate of yeast autolysate and sucrose consumption, the rate of accumulated consumption of these foods, and thus the time taken to consume the amount of yeast autolysate known to be required for the attainment of sexual maturity. Consumption rate changed within 1 or 2 days of a change between a gonadotrophic regime and a non‐gonadotrophic one (or vice versa), which is consistent with the known rapid effects of temperature change on ovarian maturation.     

Studies on the control of mitotic activity

Summary A tetraploid cell population was produced in the primary root meristem of Pisum sativum by one-half hour treatments with various concentrations of colchicine. The tetraploid population so produced was found to be reasonably synchronous in its passage through successive mitotic cycles with the degree of synchrony being more or less proportional to the concentration of colchicine used. The average time between mitoses appears to be of the order of 12 hours which agrees well with previous estimates. Treatments of roots containing tetraploid populations with 2.52 × 10^–5 M. actidione for 15 minutes were used to demonstrate the possibility of using the system for studies on the differential susceptibility of cells at different stages of the mitotic cycle.This work was carried out under contract number RG-4835 of the National Institutes of Health, United States Public Health Service, and an Institutional Grant from the American Cancer Society.Contribution number 59-26 of the Department of Botany and Plant Pathology, Michigan State University, East Lansing, Michigan.Predoctoral Fellow (CF-9871) of the National Cancer Institute, United States Public Health Service     

Ovarian maturation of Penaeus subtilis (Decapoda: Penaeidae): A new insight to describe oocyte development and somatic structures

We observed the presence of follicular cells (FC) in the ovaries of Penaeus subtilis (n = 1198), which led us to classify the development of germ cells into six phases: oogonia, previtellogenic oocytes, primary and secondary vitellogenic oocytes, mature oocytes and atretic oocytes. The FC changes their shape according to the development of germ cells and showed a different distribution along the ovary, which allowed differentiating vitellogenic oocytes into primary and secondary. We also observed that the postovulatory follicles (POF) are composed of follicular cells. The presence of POF in penaeids ovaries is rarely reported, but allows the differentiation between spent and resting stages, commonly grouped in reproductive biology research. Furthermore, observation of ovarian lining was useful to differentiate immature females from females that had spawned at least once. Thus, ovarian development was classified into six stages: immature, early developing, advanced developing, ripe, spent and resting. The distribution and shape variations of FC, ovarian lining features and presence of POF were considered crucial for the classification of ovarian maturation stages. The methods developed here may improve estimates of their reproductive cycle, size at first maturity and spawning season, which are important variables in future studies of the reproductive dynamics.     

Distribution of insoluble polysaccharides, neutral lipids, and proteins in the developing anthers of Campsis radicans (L.) Seem. (Bignoniaceae)

In this study, distribution of polysaccharides, lipids, and proteins in the developing anthers of Campsis radicans (L.) Seem. was examined from sporogenous cell stage to mature pollen, using cytochemical methods. To detect the distribution and dynamic changes of insoluble polysaccharides, lipid bodies, and proteins in the anthers through progressive developmental stages, semi-thin sections of anthers at different developmental stages were stained with periodic-acid-Schiff (PAS) reagent, Sudan black B, and Coomassie brilliant blue, respectively, and examined under light microscope. Ultrastructural observations with TEM were also carried out to determine the storage form of starch in the connective tissue, and storage form of lipids in the tapetal cells. In sporogenous cell stage, anther wall contains numerous insoluble polysaccharides. However, from the sporogenous cell stage to the vacuolated microspore stage, the amount of insoluble polysaccharides in the anther wall decreases gradually. At bicellular pollen stage, tapetum degenerates completely and polysaccharides are not seen in the anther wall. Lipid bodies are observed in the cytoplasm of both middle layer and tapetal cells at tetrad stage, whereas they disappear in the vacuolated microspore stage. Compared with polysaccharides, proteins are limited in the anther wall at early stages of development. During pollen development, polysaccharides, proteins, and lipid bodies are scarce in the cytoplasm of sporogenous cells, but their amount increases at premeiotic stage. From tetrad stage to bicellular pollen stage, microspore cytoplasm contains variable amount of insoluble polysaccharide grains, lipid and protein bodies. At bicellular pollen stage, plentiful amount of starch granules are stored in the cytoplasm of the pollen grains. Proteins and lipid bodies are also present in the cytoplasm.     

Expression and Effects of Hyaluronan and of the Hyaluronan-Binding Protein Hyaluronectin in Newborn Rat Brain Glial Cell Cultures

Abstract: Hyaluronan (HA) is a polymerized nonsulfated extracellular matrix glycosaminoglycan that may be involved in brain development. We have tested the expression of HA and the HA-binding protein hyaluronectin (HN) in glial cell cultures from newborn rat brain. HA was secreted into the culture medium by type 1 astrocytes in the first stages of the primary cultures. The secretion was high during cell proliferation, reached a maximum when they were confluent, and then decreased. HA was not secreted at a detectable level by total O-2A lineage cell- enriched cultures. HA labeled small O-2A progenitor cells (GFA-, A2B5⁺, HA⁺), small O-2A progenitorlike (GFA^?, A2B5^?, HA⁺) cells, and type 2 astrocytes (GFA⁺, A2B5⁺, HA⁺), but not mature oligodendrocytes (Galc⁺, HA^?). In contrast to HA, hyaluronectin labeled oligodendrocyte membranes (i.e., more mature cells) from day 8. A2B5⁺ GFA^? cells were found to be either HA⁺ or HN⁺ at days 7–9, suggesting intermediary stages. The addition of HA to primary cultures and to O-2A progenitor-enriched cultures decreased significantly the increase in the number of O-2A progenitors, of mature (Galc⁺) oligodendrocytes proportionally to the decrease of the O-2A progenitor number, and of BrdU⁺ cells, suggesting that HA acts (directly or indirectly) on O-2A cell proliferation. This effect, which was seen for concentrations as low as 0.1 μg/ml, was HA specific and was not observed with other glycosaminogly- cans. When primary cultures were performed in the presence of hyaluronidase-digested or HA-depleted (by passage on a HN column) fetal calf serum, the total number of O-2A lineage cells was dramatically increased (100%, p<10–⁴) in comparison with control cultures in standard fetal calf serum. Platelet-derived growth factor increased the total number of O-2A lineage cells and of (Galc⁺) oligodendrocytes. This effect was opposed by HA dose dependently. The effect of HA was significantly inhibited by HN (30%, p<10–⁴). HN had, however, no effect when it was added to culture in the presence of hyaluronidase in fetal calf serum, suggesting its effect was only due to its binding to HA. During cell maturation, HA disappears as HN appears. This and the fact that HA and PDGF have opposite effects suggest an effect of these factors, or of their balance, on myelination.     

Occurrence of a New Microsporidan: Enterocytozoon bieneusi n. g., n. sp., in the Enterocytes of a Human Patient with AIDS1

A new microsporidium is reported infesting the enterocytes of a Haitian patient with AIDS. The stages observed were diplokaryotic cells, sporogonial plasmodia, unikaryotic sporoblasts, and spores. Neither a sporophorous vesicle (pansporoblastic membrane) nor parasitophorous vacuole were differentiated around the developmental stages, which were in direct contact with the host cell cytoplasm. The polar tube (5-6 coils) was differentiated before fission of the sporogonial plasmodium. The mature spores measured 1.5 m?m × 0.5 m?. The spore wall was very thin as the endospore was absent or poorly differentiated. The organism is named Enterocytozoon bieneusi n. g., n. sp. and is assigned to the suborder Apansporoblastina.     

Growth and accumulation of storage reserves by somatic embryos of Ocotea catharinensis Mez. (Lauraceae)

The focus of this study was the assessment of in vitro growth of embryogenic cultures of Ocotea catharinensis Mez. (Lauraceae) on Woody Plant Medium (WPM) supplemented with 22.7 g l^–1 sorbitol, 2 g l^–1 Phytagel, 20 g l^–1 sucrose and 400 mg l^–1 glutamine and the biochemical analysis of somatic embryos at different developmental stages (globular, early cotyledonary, cotyledonary and mature). The embryoids underwent repetitive embryo-genesis and developed non-synchronously, throughout the culture period. Dry weight increased 12.6- and 26.8-fold after 3 and 5 weeks, respectively. During the 5 week culture period a reduction in the frequency of embryoids at the globular stage and increasing frequencies of embryoids at early cotyledonary, cotyledonary and mature stages were observed. Embryoids at the mature stages presented a small but significantly higher water content than those at the globular stage. Therefore, embryoid expansion at the latter stages of development was mainly due to water uptake. Embryoids at the globular stages accumulated higher levels of total proteins while those at the cotyledonary and mature stage showed higher levels of soluble sugars and starch (physiological markers of embryo maturation). Thus, significant differences in the profiles of accumulated storage reserves were detected in the embryoids at different developmental stages in the culture conditions tested.     

Ultrastructural and cytochemical studies on the germarium of Dicrocoelium dendriticum (Plathelminthes,Digenea)

Summary The unpaired germarium of Dicrocoelium dendriticum contains many female germ cells at different stages of maturation and is enveloped by a fibrous basal lamina-like structure and a multilayered cytoplasmic sheath whose origins and functions are discussed. The maturation process of primary oocytes occurs completely within the prophase of the first meiotic division. It has been divided into three stages, as previously suggested for monogeneans. Stage I corresponds to oogonia and early oocytes which are located in the distal germinative area of the gonad. These cells are characterized by a high nucleo/cytoplasmic ratio and a poorly differentiated cytoplasm. Stage II corresponds to maturing oocytes grouped in the central area of the gonad and exhibiting long synaptonemal complexes and a prominent nucleolus. The main feature of cytoplasmic differentiation is the increase in the number of RER and Golgi complex which are involved in the production of small electron-dense granules. Stage III corresponds to mature oocytes located in the proximal area of the germarium near the origin of the oviduct. In this stage, the granules become regularly distributed in a monolayer in the peripheral ooplasm and make contact with the oolemma. They show a distinctive complex structure, are composed of proteins and glycoproteins and do not contain polyphenols. Their possible role as cortical granules is discussed in relation to chemical composition and previous studies on other Plathelminthes. Neither yolk globules nor glycogen are present in the oocytes.Abbreviations I oogonium and early oocyte - II growing oocyte - III mature oocyte - cg cortical granule - cs cytoplasmic sheath - db dense body - ecm extra cellular matrix - ER endoplasmic reticulum - fl fibrous extracellular layer - gc Golgi complex - m mitochondria - N nucleus - nu nucleolus - RER rough endoplasmic reticulum - sc synaptonemal complex