How Do You Find Eel Gonads

Cholesterol (pmol 1_1)

4020 ±142

Phosphatidylcholine (pmol 1_1)

47.98 ±31.92

Choline (pmol 1~')

732.43 ± 355.66

Alkaline phosphatase (pmol min 1 1_1)

32.79 ±4.11

Acid phosphatase (pmol min11_1)

3.98 ± 1.34

ß-d-glucuronidase (pmol min11_1)

0.46 ± 0.32

Protease (gelatin substrate) (pmol min11_1)

34.59 ± 25.72

Protease (casein substrate) (pmol min11_1)

14.43 ±11.21

cle comprises most of the thickness of the ovarian wall; the fibres are arranged roughly into two layers: an inner circular and an outer longitudinal (Figure 1.41C). Small blood vessels course between the muscle cells as well as bundles of unmyelinated nerves that tend to run parallel to the long axis of the ovary. Vascular connective tissue of variable thickness occurs between the muscle cells and ovarian follicles. It is suggested that ovulation is accompanied by a wave of contraction of this smooth muscle, coordinated by nervous elements, that squeezes eggs from the lumen, beginning crani-ally and proceeding caudally.

The germinal ridges extend the length of the ovary and contain the proliferative stem cells from which the oocytes are derived and follicles formed (Figure 1.42A). The ridges are covered by the luminal epithelium of squamous to cuboidal cells and contain richly vascular connective tissue surrounding each follicle, especially the largest; extensive lymphatic spaces, lined by attenuated endothelial cells, penetrate this stroma (Figure 1.42B). The developing follicles migrate from the germinal ridges and constitute the follicular lamina of the ovarian sheet.

As in many bony fishes, the lumen of these cys-tovarian ovaries is lined by an epithelium that is derived from the coelomic mesothelium and is continuous with the oviduct. The epithelial cells lie on a distinct basal lamina and vary in shape from squamous over the germinal ridge to cuboidal or columnar over more mature follicles (Figure 1.43). The apical surfaces may display microvilli, lateral surfaces are highly interdigitated, and there may be basal infoldings of the plasmalemma. Blebs from the apical surface may protrude into the lumen (Figure 1.44). Within the epithelial cells are abundant cytoplasmic filaments and the cells are attached to one another laterally by desmo-somes and apically by tightjunctions.

A form of apocrine secretion has been described in some of the columnar epithelial cells of the ovarian lumen of two other species of teleosts. (During apocrine secretion, part of the cell is lost.) Following ovulation in the medaka Oryzias latipes, apical "blebs" break off from the rest of the cell and contribute to the secreted material in the lumen (Takano, 1968). There are no microvilli on these special cells and irregular processes containing vacuoles (presumably derived from the Golgi complex) form on their apical surfaces (Figure 1.45A). The processes break off, thereby forming the apocrine secretion. This activity ceases after ovulation and the cytoplasm of the epithelial cells becomes more electron lucent. As the ovary matures in the goldfish Carassius auratus, the dorsal epithelial cells develop cilia and large cytoplasmic blebs break away from the surface at the bases of the cilia (Figure 1.45B) (Taka-hashi and Takano, 1971). It is suggested that the apocrine secretions contribute to the maintenance of the ovulated eggs within the lumen and that the cilia assist in transporting them to the oviduct.

An unusual adaptation is seen in some species of Scorpaeniformes where the lining of the hollow ovary secretes a bilobed, gelatinous mass that provides protection for the eggs (Fishelson, 1977; Erickson and Pikitch, 1993; Koya, Hamatsu, and Matsubara, 1995; Koya and Matsubara, 1995). The paired cystovarian ovaries are sheathed within a wall of smooth muscle and connective tissue and are enclosed by visceral peritoneum. The ovarian walls converge caudally as an oviduct that terminates between the urinary pore and the anus. Anteriorly the ovaries are rounded and each of them is suspended by a spongy, vessel-rich hi-lus whose vessels penetrate into the lumen to enter the spongy, vascular, ovigerous stroma,. Suspended by the hilus at the anterior end of each lobe, the ovigerous stroma floats free within the lumen. The ovigerous tissue is covered by an oocyte-producing epithelium that bristles with vascularized "peduncles" that radiate from the stroma (Figures 1.46A,B). These peduncles are extensions of the stroma and accommodate secondary oocyte development (Figures 1.46C,D). Each oocyte is enclosed by its amorphous zona pellucida, a layer of follicular cells, and a theca (Figure 1.46E).

The luminal wall is lined by a simple columnar epithelium; a more delicate simple columnar epithelium covers the ovigerous tissue. During the spawning season, the epithelial cells of both surfaces secrete the gelatinous mass that fills the lumen. These columnar cells increase in height from vitellogenesis to maturation; they decline after ovulation. The gelatinous mass occurs in two layers: a fibrous outer layer of polysaccharide and lipid and a homogeneous inner layer of glycolipoprotein or proteoglycan associating lipid. The outer, fibrous layer is secreted by the larger, columnar epithelial cells of the ovarian wall. These cells contain abundant agranular endoplasmic reticulum and release apical blebs into the lumen (Figures 1.47A,B). The columnar cells of the ovigerous epithelium secrete the inner layer and are rich in agranular and granular endoplasmic reticulum and Golgi complexes (Figure 1.47C). They release materials by exo-cytosis.

Peduncle length increases as vitellogenesis proceeds. Within the base of each peduncle are previtel-logenic oocytes; when a mature oocyte is released at ovulation, a previtellogenic oocyte moves up inside the peduncle to take its place and undergo vitellogenesis. At ovulation, the oocytes, embedded in the gelatinous mass, are swept from the lumen (Figure 1.48). The gelatinous mass, secreted by the epithelia of the two lobes, is extruded around the ovigerous tissue of both lobes to form the hollow, bilobed egg mass. Three features of these unusual ovaries facilitate the production, shaping, and expulsion of these egg masses: the ovigerous stroma is encircled by oocytes and connected to the ovarian wall only at the anterior end of each lobe; the inner ovarian wall is lined with secretory cells; and vitellogenic oocytes are borne on peduncles that extend into the lumen, becoming embedded in the gelatinous mass. Similar adaptations for the production of gelatinous egg masses have been described in the masked greenling Hexagrammos oc-togrammus (Scorpaeniformes) (Koya, Munehara, and Takano, 1993) and the angler fish Lophiomus setigerus (Lophiiformes) (Yoneda et al., 1998).

Several marine cottid species (Scorpaeniformes) have a unique reproductive mode called "internal gametic association" where spermatozoa are introduced into the ovarian cavity by copulation and float freely in the ovarian fluid although fertilization does not occur until the eggs have been spawned into sea water (Koya, Takano, and Takahashi, 1995; Koya, Munehara, and Takano, 1997). The lumen of the ovarian cavity is lined with a simple microvillous epithelium that secretes the ovarian fluid but does not appear to have a specialized structure for sperm storage (Figures 1.49A,B). During the spawning period, the epithelial cells of both the ovigerous lamellae and the luminal wall manifest the appearance of protein production with abundant basal granular endoplasmic reticulum and active apical Golgi complexes (Figures 1.49C to E). Numerous pinocytotic pits and vesicles are seen in the peripheral cytoplasm of these cells; increasing numbers of pits and vesicles are also present in the endothelial cells of adjacent capillary walls at this time indicating that active transcytosis is taking place (Figure 1.49F). Substances transported from the capillaries appear to be taken into the epithelial cells by endocytosis and synthesized in the granular endoplasmic reticulum into materials that are accumulated in the secretory vesicles by way of the Golgi complexes to be released into the ovarian cavity by exocytosis.

These secretions may be augmented by microapocrine secretions wherein blebs are released from projections of the apical surfaces of the epithelial cells (Figures 1.49C,E). This secretory activity shows distinct seasonal changes, being most active during the spawning period, declining during the degeneration period to become quiescent during the recovery period. Adjacent epithelial cells are joined by junctional complexes (Figure 1.49G) and it is suggested that these tight junctions isolate the spermatozoa in the lumen from the maternal immune system. After the spawning period, thejunctions break down and residual spermatozoa are eliminated by invading maternal leucocytes: plasma cells, polymorphonuclear leucocytes, and monocytes/macrophages (Figure 1.49H). A summary of the cyclic changes in these epithelial is shown in Figure 1.491.

The mature ovaries of Chondrichthyes are surrounded by the gonadal epithelium and consist of a connective tissue stroma containing developing follicles, postovulatory follicles (corpora lutea), and degenerating follicles (corpora atretica) (Stanley, 1963; Wourms, 1977; Callard et al., 1989; Hamlett and Koob, 1999). Blood vessels and nerves course through the stroma. The stroma also contains lymph spaces or membranous folds that are filled with developing blood cells (Figure 1.50). Although ovarian morphology is variable in Chondrichthyes, differences are superficial and attributable largely to the numbers and sizes of the yolky eggs present (TeWinkel, 1972; Dodd, 1983; Callard et al., 1989). Variations are related not only to the stage of the reproductive cycle, but also to the mode of reproduction of the species: whether oviparous or viviparous. Vitellogenic oocytes dominate the gross appearance of the ovary of repro-ductively active females (Callard et al., 1989). After ovulation, the volume of the ovary is greatly reduced and it contains only smaller follicles, corpora lutea, and corpora atretica.

Yellowish, irregular masses of haemopoietic tissue, the epigonal organs, are associated with the gonads of elasmobranchs (Figures 1.16 and 1.17) (Fänge, 1977; Fänge and Mattisson, 1981; Zapata, 1981; Fänge and Pulsford, 1983; Zapata et al., 1996). Although sometimes reduced to the point that they are detectable only by microscopic examination, they have been found in all species examined. They occur in the mesovarium and, in young specimens of Scyliorhinus canicula, are said to surround the ovary. Aggregations of haemopoietic tissue in the ovarian stroma of some elas-

mobranchs are probably rudimentary epigonal organs (Figure 1.51) (Fänge, 1977). In the basking shark, Cetorhinus maximus, where only the right ovary persists, the epigonal organ lies posterior and slightly dorsal to the ovary, being suspended from the dorsal abdominal wall by a backward extension of the mes-ovarium (Figure 1.16) (Matthews, 1950). The left epi gonal organ is of similar size and shape as the right but no ovary is fused to its anterior end and it is suspended by its own peritoneal fold in the corresponding position on the left side of the body cavity (Figure 1.52). No haemopoietic tissue is associated with the urino-genital system of the holocephalan Hydrolagus colliei (Stanley, 1963).

Urino Genital System Tilapia

Figure 1.1: Ovaries and testes develop from paired masses of mesodermal tissue on either side of the dorsal mesentery in the dorsolateral lining of the peritoneal cavity. These indifferent genital ridges bulge into the developing coelom and are later invaded by primordial germ cells (arrows) that will eventually give rise to oogonia or spermatogonia. Six stages of this migration are shown in these photomicrographs of cross sections of embryos Oryzias latipes. Bar = 40 |im (From Hamaguchi, 1982; reproduced with permission of the author).

A. Primordial germ cells (PGCs) shown in the peripheral endoderm.

B. The PGCs lie alongside the newly-formed gut.

C. The PGCs come together between the lateral plate mesoderm and ectoderm. As the lateral plate mesoderm differentiates into splanchnic and somatic mesoderm, the PGCs migrate through the somatic mesoderm to the dorsal mesentery.

D. Some germ cells have reached the gonadal region, others are in the somatic mesoderm.

E. All germ cells have arrived in the gonadal anlage between the pronephric duct and the gut.

F. One of the germ cells is undergoing mitosis.

Abbreviations: n, neural tube; m, mesoderm; ent, entoderm; g, gut; p, pronephric duct.

Figure 1.1: Ovaries and testes develop from paired masses of mesodermal tissue on either side of the dorsal mesentery in the dorsolateral lining of the peritoneal cavity. These indifferent genital ridges bulge into the developing coelom and are later invaded by primordial germ cells (arrows) that will eventually give rise to oogonia or spermatogonia. Six stages of this migration are shown in these photomicrographs of cross sections of embryos Oryzias latipes. Bar = 40 |im (From Hamaguchi, 1982; reproduced with permission of the author).

A. Primordial germ cells (PGCs) shown in the peripheral endoderm.

B. The PGCs lie alongside the newly-formed gut.

C. The PGCs come together between the lateral plate mesoderm and ectoderm. As the lateral plate mesoderm differentiates into splanchnic and somatic mesoderm, the PGCs migrate through the somatic mesoderm to the dorsal mesentery.

D. Some germ cells have reached the gonadal region, others are in the somatic mesoderm.

E. All germ cells have arrived in the gonadal anlage between the pronephric duct and the gut.

F. One of the germ cells is undergoing mitosis.

Abbreviations: n, neural tube; m, mesoderm; ent, entoderm; g, gut; p, pronephric duct.

Epigonal Organ Nerves Histology

Figure 1.2: Electron micrographs of cross sections through the developing gonad of the eel Anguilla anguilla containing primordial germ cells (PGC1) enveloped by somatic cells (SC). The gonad is enclosed by peritoneal epithelium (PEC, GPE) formed of flattened cells on the medial side (MS) and thicker cells on the lateral side (LS). A: 6.8 cm elver; X 3,800. B: 10.6 cm eel; X 2,800. (From Grandi and Colombo, 1997; © reproduced with permission of John Wiley & Sons, Inc.).

Figure 1.2: Electron micrographs of cross sections through the developing gonad of the eel Anguilla anguilla containing primordial germ cells (PGC1) enveloped by somatic cells (SC). The gonad is enclosed by peritoneal epithelium (PEC, GPE) formed of flattened cells on the medial side (MS) and thicker cells on the lateral side (LS). A: 6.8 cm elver; X 3,800. B: 10.6 cm eel; X 2,800. (From Grandi and Colombo, 1997; © reproduced with permission of John Wiley & Sons, Inc.).

Pgcs Visceral Ectoderm HumanPlasma Membrane Follicle Cell Ovary

Figure 1.3: Diagrammatic representation of the germinal epithelium and the process of oogenesis from a single oogonium in the common snook Centropomus undecimalis. Germ cells are yellow and orange; epithelial prefollicle cells and follicle cells are blue; cells within the stroma are green; the basement membrane is red. The germinal epithelium extends between the basement membrane (BM) and the ovarian lumen (OL). It is composed of somatic cells (epithelial cells, E, which become prefollicle cells, PF, during folliculogenesis) and germ cells (oogonia, OG, and pachytene, P, and diplotene oocytes). Oogonia may divide mitotically to maintain their population within the germinal epithelium (mitosis, arrows). They may enter into meiosis, becoming oocytes, and move away from the ovarian lumen. At the initiation of meiosis, the process of folliculogenesis commences (meiosis, arrows). Folliculogenesis is completed when the basement membrane extends up over the forming follicle, its diplotene oocyte, and prefollicle cells, and pinches the follicle off from the germinal epithelium. Prefollicular cells then become follicular cells (F). While within the germinal epithelium, or attached to a cell nest, the oocyte primary growth phase commences when RNA-rich cytoplasm (RC) begins to appear during diplotene. RNA continues to accumulate as both the nuclear and cytoplasmic volumes increase after completion of folliculogenesis coupled with the appearance of multiple nucleoli (NU) and their final orientation around the periphery of the nucleus (N) (perinucleolar stage). Folliculogenesis is complete before this stage of maturation is reached. Beside an RNA-rich cytoplasm, mitochondria (M) and other cellular organelles begin to appear in the oocyte cytoplasm. The follicle is composed of the diplotene oocyte and an encompassing layer of follicular cells. It is separated from the stroma by a basement membrane. In the stroma, prethecal cells (PT) within the extravascular space (EVS) associate with the follicle and form the theca interna. During primary growth, undifferentiated cells within the EVS associate with the surface of the theca. They differentiate into a theca externa (TE). Blood vessels (BV) also reside within the EVS. (From Grier, 2000; © reproduced with permission of John Wiley & Sons, Inc.).

Figure 1.4: Primordial germ cells (PGC) arise early in development within embryonic endoderm (end) or mesoderm (mes), long before the rudiments of the gonads are formed and at a distance from the site they will eventually occupy. Photomicrographs of cross sections at the level of the anterior somites through 12-hour embryos of Barbus conchionus. (From Timmer-mans and Taverne, 1989; © reproduced with permission of John Wiley & Sons, Inc.).

Abbreviations: ch, chorda mesoderm; ect, ectoderm; evl, enveloping layer; p, periblast; y, yolk.

Cyprinus Carpio Blood Cells

Figure 1.5: The site of origin of primordial germ cells is extragonadal and, in some fishes, may be extraembryonic. These cells migrate into the rudimentary gonad and establish residence in the outer margin of the stroma, just beneath the gonadal epithelium. These are schematic drawings of sections through the carp Cyprinus carpio showing male and female gonads during development. (From Parmentier and Timmermans, 1985; reproduced with permission from the Company of Biologists, Ltd.).

A. Indifferent gonad at 8 weeks.

B. Male gonad at 15 weeks.

C. Female gonad at 15 weeks.

Abbreviations: bv, blood vessel; cc, cyst cell; epo, early prophase oocytes; it, interstitial tissue; Oo, oogonia; mPGC, mitotic primordial germ cell; sg, spermatogonia.

Figure 1.5: The site of origin of primordial germ cells is extragonadal and, in some fishes, may be extraembryonic. These cells migrate into the rudimentary gonad and establish residence in the outer margin of the stroma, just beneath the gonadal epithelium. These are schematic drawings of sections through the carp Cyprinus carpio showing male and female gonads during development. (From Parmentier and Timmermans, 1985; reproduced with permission from the Company of Biologists, Ltd.).

A. Indifferent gonad at 8 weeks.

B. Male gonad at 15 weeks.

C. Female gonad at 15 weeks.

Abbreviations: bv, blood vessel; cc, cyst cell; epo, early prophase oocytes; it, interstitial tissue; Oo, oogonia; mPGC, mitotic primordial germ cell; sg, spermatogonia.

Cyprinus Carpio Blood Cells

Figure 1.6: Primordial germ cells are ensheathed by cells derived from the gonadal epithelium. Schematic drawings of cross sections through gonadal primordia of the common carp Cyprinus carpio at 1, 3, and 5 weeks. (From van Winkoop et al., 1992; reproduced with permission from Springer-Verlag).

A. In the first week the primary germ cell is enclosed by extensions of one or two somatic cells; these form junctional complexes at the side of the coelomic cavity but not at the dorsal side. The outlined area is shown in Figure D.

B. By the third week, the number of somatic cells surrounding the primary germ cell has increased. The outlined area is shown in Figure E.

C. In the fifth week, a central layer of lighter cells, located close to the primary germ cells, is surrounded by a layer of darker peripheral cells. The upper outlined area is shown in Figure F and the lower area is shown in Figure H.

Figure 1.6: Continued.

Figures D to H are electron micrographs of cross sections through primary germ cells and gonadal primordia.

D. At 3 days a primary germ cell is enveloped by dorsal extensions of a somatic cell (so). Part of the nucleus (n) is shown. Perinuclear dense bodies (PDB), located near nuclear pores (po), are associated with mitochondria (m). The cytoplasm contains agranular endoplasmic reticulum (ER). Bar=l |im.

E. A primary germ cell at 3 weeks contains light (1) and dark (d) material; the latter adheres to a mitochondrion (m). Note junctional complexes (arrows) between the extensions of somatic cells (so). The nucleus (n) is at the left. Bar = 1 pm.

F. (upper outline in Figure C). Primary germ cell at 4 weeks. Dark cement (cm) is associated with mitochondria (m). Long, agranular cisternae of the endoplasmic reticulum (ER) lie parallel to the cell membrane. The nucleus (n) is at the left. Bar = 1 |im.

G. A primary germ cell (PGC) enveloped by somatic cells at 5 weeks. (The nucleus of the primary germ cell is not visible.) The lighter central somatic cells (c) are surrounded by darker peripheral cells (p). Bar = 10 |im.

H. (lower outline in Figure C). Enveloping somatic cells at 5 weeks. Both the lighter central cells (c) and the peripheral cells (p) rest on basement membranes (bm) with connective tissue between. Bar = 1 pm.

Figure 1.7: Electron micrographs of sections of primordial germ cells of Oryzias latipes. (From Hamaguchi, 1982; reproduced with permission of the author).

A. Primary germ cells (g) are larger than surrounding cells, are rounded, oval, or pear-shaped, and show a distinct cell boundary. They are surrounded by somatic cells (m) rich in ribosomes. Pronephric duct, p. Bar = 10 |im.

B. Mesodermal cells surround the primordial germ cell (gdb). The nuclear material is homogeneous. There is a large, round, conspicuous nucleolus. The surrounding somatic cells are richer in ribosomes. Bar = 2 |im.

Figure 1.7: Electron micrographs of sections of primordial germ cells of Oryzias latipes. (From Hamaguchi, 1982; reproduced with permission of the author).

A. Primary germ cells (g) are larger than surrounding cells, are rounded, oval, or pear-shaped, and show a distinct cell boundary. They are surrounded by somatic cells (m) rich in ribosomes. Pronephric duct, p. Bar = 10 |im.

B. Mesodermal cells surround the primordial germ cell (gdb). The nuclear material is homogeneous. There is a large, round, conspicuous nucleolus. The surrounding somatic cells are richer in ribosomes. Bar = 2 |im.

Wiley Barnard

Figure 1.8: Electron micrographs of sections of primordial germ cells of the eel Anguilla anguilla. (From Grandi and Colombo, 1997; © reproduced with permission of John Wiley & Sons, Inc.).

A. A primordial germ cell has a nucleus (NG) with irregular outline, a few long cisternae of endoplasmic reticulum (ER), "nuage" (n), a cluster of mitochondria (M) in the cytoplasm, coated pits (arrow), and microvillous extensions (Mv) of the border. An enveloping somatic cell has a flattened nucleus (NE) and many bundles of microfilaments in the cytoplasm. Note the desmosome (D) between the primordial germ cell and the somatic cell. X14,800.

B. Details of a primordial germ cell showing a Golgi complex (G), centriole (Ct), and other organelles. Labelling as in Figure 8A. X16,400.

Figure 1.8: Electron micrographs of sections of primordial germ cells of the eel Anguilla anguilla. (From Grandi and Colombo, 1997; © reproduced with permission of John Wiley & Sons, Inc.).

A. A primordial germ cell has a nucleus (NG) with irregular outline, a few long cisternae of endoplasmic reticulum (ER), "nuage" (n), a cluster of mitochondria (M) in the cytoplasm, coated pits (arrow), and microvillous extensions (Mv) of the border. An enveloping somatic cell has a flattened nucleus (NE) and many bundles of microfilaments in the cytoplasm. Note the desmosome (D) between the primordial germ cell and the somatic cell. X14,800.

B. Details of a primordial germ cell showing a Golgi complex (G), centriole (Ct), and other organelles. Labelling as in Figure 8A. X16,400.

Figure 1.9: Electron micrograph of a section through the cytoplasm of a primordial germ cell of the carp Cyprinus carpio of 5 weeks. One coated vesicles (cv) vesicle has fused with the plasma membrane and opens into the narrow intercellular space adjacent to a somatic cell (so). Bar = 0.1 |im. (From van Winkoop et al., 1992; reproduced with permission from Springer-Verlag).

Intercellular Ridge

Figure 1.10: Electron micrograph of a section of the indifferent gonad of the genital ridge of Oryzias latipes. Two cytoplasmic markers distinguish primordial germ cells from somatic cells (Pn). These are thin sheets of agranular endoplasmic reticulum (arrows) and electron-dense mitochondrial associated granular material (MAGM). X 4,700 (From Hogan, 1978; reproduced with permission from Elsevier Science).

Figure 1.10: Electron micrograph of a section of the indifferent gonad of the genital ridge of Oryzias latipes. Two cytoplasmic markers distinguish primordial germ cells from somatic cells (Pn). These are thin sheets of agranular endoplasmic reticulum (arrows) and electron-dense mitochondrial associated granular material (MAGM). X 4,700 (From Hogan, 1978; reproduced with permission from Elsevier Science).

Electron Photomicrographs Mitochondria

Figure 1.11: These electron micrographs show changes in the appearance of mitochondrial-associated granular material in premigratory germinal cells of Oryzias latipes as the cells begin their migration to the gonadal anlagen. X 45,000 (From Hama-guchi, 1985; reproduced with permission of the author).

A. As the cells begin their migration, the material is loosely-woven and strandlike.

B. This appearance gradually changes as a small, amorphous mat of fine, electron-dense fibrils forms.

C. The amorphous mat becomes dominant.

D. The material has become an amorphous body of fine, electron-dense fibrils. In the gonadal anlagen, these bodies are amorphous, of various sizes and shapes. Bar = 0.2 |im.

Figure 1.11: These electron micrographs show changes in the appearance of mitochondrial-associated granular material in premigratory germinal cells of Oryzias latipes as the cells begin their migration to the gonadal anlagen. X 45,000 (From Hama-guchi, 1985; reproduced with permission of the author).

A. As the cells begin their migration, the material is loosely-woven and strandlike.

B. This appearance gradually changes as a small, amorphous mat of fine, electron-dense fibrils forms.

C. The amorphous mat becomes dominant.

D. The material has become an amorphous body of fine, electron-dense fibrils. In the gonadal anlagen, these bodies are amorphous, of various sizes and shapes. Bar = 0.2 |im.

Squama Cyprinus Carpio

Figure 1.12: In the carp Cyprinus carpio the mitochondrial associated granular material increases in size with development and part becomes more electron dense forming dark masses that adhere to mitochondria and may be centres for mitochondrial multiplication. Bar = 1 pm. (From van Winkoop et al., 1992; reproduced with permission from Springer-Verlag).

A. A primordial germ cell at 3 days, showing part of the nucleus (n). The cytoplasm contains agranular endoplasmic reticulum (ER). A dense body (PDB) and associated mitochondrion (m) lies near a nuclear pore (po). Surface membrane of primordial germ cell pi; dorsal extension of enveloping somatic cell, so.

B. Two types of dense material are seen in primordial germ cells at 3 weeks: light (1) and dark (d), the latter adhering to a mitochondrion (m). At the right,junctional complexes (arrows) link extensions of the surrounding somatic cells.

Figure 1.12: In the carp Cyprinus carpio the mitochondrial associated granular material increases in size with development and part becomes more electron dense forming dark masses that adhere to mitochondria and may be centres for mitochondrial multiplication. Bar = 1 pm. (From van Winkoop et al., 1992; reproduced with permission from Springer-Verlag).

A. A primordial germ cell at 3 days, showing part of the nucleus (n). The cytoplasm contains agranular endoplasmic reticulum (ER). A dense body (PDB) and associated mitochondrion (m) lies near a nuclear pore (po). Surface membrane of primordial germ cell pi; dorsal extension of enveloping somatic cell, so.

B. Two types of dense material are seen in primordial germ cells at 3 weeks: light (1) and dark (d), the latter adhering to a mitochondrion (m). At the right,junctional complexes (arrows) link extensions of the surrounding somatic cells.

Transverse Section Ovary Fish

Figure 1.13: The ovaries are suspended in the posterior body cavity, dorsal to the gut, by mesovaria that run their entire length. Diagrammatic cross sections through the body of an adult female shark Scyliorhinus canicula. X 1 (From Metten, 1939; reproduced with permission from the Royal Society).

A. Section through the posterior end of the stomach.

B. Section through the duodenum.

Figure 1.13: The ovaries are suspended in the posterior body cavity, dorsal to the gut, by mesovaria that run their entire length. Diagrammatic cross sections through the body of an adult female shark Scyliorhinus canicula. X 1 (From Metten, 1939; reproduced with permission from the Royal Society).

A. Section through the posterior end of the stomach.

B. Section through the duodenum.

Figure 1.14: The ovaries (G) may be displaced toward the intestine, coming to lie, with the intestine (D), within the mesentery. (From Harder, 1975; reproduced with permission of Schweizerbart'sche Verlagsbuchhandlung, www.schweizerbart.de).

Mesonephric Duct Aquatic Animals

Figure 1.15: In elasmobranchs, a duct system typical of higher vertebrates develops from the mesonephric or Mullerian ducts, gathering up shed eggs or embryos in a funnel-shaped ostium and passing them through an oviduct to the outside, often adding a shell or providing refuge for developing embryos along the way. (From Hoar, 1969; reproduced with permission from Elsevier Science).

Figure 1.15: In elasmobranchs, a duct system typical of higher vertebrates develops from the mesonephric or Mullerian ducts, gathering up shed eggs or embryos in a funnel-shaped ostium and passing them through an oviduct to the outside, often adding a shell or providing refuge for developing embryos along the way. (From Hoar, 1969; reproduced with permission from Elsevier Science).

Figure 1.16: Although the ovaries of most elasmobranchs are solid, the visceral peritoneal covering of the ovary of lamnid sharks invaginates to create a hollow organ. The hollow is a direct extension of the peritoneal cavity and forms a branching invagination from a pocket on the right side of the outer surface. Shown is the right ovary and epigonal organ, seen from the right side, of the basking shark Cetorhinus maximus. Only the right ovary persists and the epigonal organ lies posterior and slightly dorsal to the ovary, being suspended from the dorsal abdominal wall by a backward extension of the mesovarium. The pocket leading to the interior is visible on the right side. (From Matthews, 1950; reproduced with permission from the Royal Society).

Figure 1.16: Although the ovaries of most elasmobranchs are solid, the visceral peritoneal covering of the ovary of lamnid sharks invaginates to create a hollow organ. The hollow is a direct extension of the peritoneal cavity and forms a branching invagination from a pocket on the right side of the outer surface. Shown is the right ovary and epigonal organ, seen from the right side, of the basking shark Cetorhinus maximus. Only the right ovary persists and the epigonal organ lies posterior and slightly dorsal to the ovary, being suspended from the dorsal abdominal wall by a backward extension of the mesovarium. The pocket leading to the interior is visible on the right side. (From Matthews, 1950; reproduced with permission from the Royal Society).

Figure 1.17: Channels penetrate all parts of the ovary and provide a means of exit for ripe oocytes. Posterior view of the ovary of a mature lamnid shark. The left illustration is diagrammatic, the right is schematic. Arrows indicate paths of the oocytes. (From Pratt, 1988; reproduced with permission of the American Society of Ichthyologists and Herpetologists).

Figure 1.17: Channels penetrate all parts of the ovary and provide a means of exit for ripe oocytes. Posterior view of the ovary of a mature lamnid shark. The left illustration is diagrammatic, the right is schematic. Arrows indicate paths of the oocytes. (From Pratt, 1988; reproduced with permission of the American Society of Ichthyologists and Herpetologists).

Cystovarian Fish

Figure 1.18: The cavity of cystovarian ovaries may be formed in two ways. (From Weichert, 1970; reproduced with permission of the McGraw-Hill Companies).

A. An endovarian cavity is derived from internalized invaginations of the genital ridges where the ribbonlike ovaries roll up in a lateral and dorsal direction so that the side at which ovulation occurs is turned inward surrounding the cavity.

B. Alternatively, a parovarian cavity arises from a space enclosed by adhesions between the genital ridge and the parietal peritoneum.

Figure 1.18: The cavity of cystovarian ovaries may be formed in two ways. (From Weichert, 1970; reproduced with permission of the McGraw-Hill Companies).

A. An endovarian cavity is derived from internalized invaginations of the genital ridges where the ribbonlike ovaries roll up in a lateral and dorsal direction so that the side at which ovulation occurs is turned inward surrounding the cavity.

B. Alternatively, a parovarian cavity arises from a space enclosed by adhesions between the genital ridge and the parietal peritoneum.

Figure 1.19: Steroid-producing cells are described in the ovary of tilapia Sarotherodon niloticus during ovarian differentiation. As the ovarian cavity is forming, these cells appear near the blood vessels of the stroma on the side facing the mesentery. These photomicrographs of cross sections of the ovary show many steroid-producing cells near the blood vessels. (From Naka-mura and Nagahama, 1985; reproduced with permission from Blackwell Publishing).

A. 35 days after hatching. Sterioid producing cells at centre left. Premeiotic oocyte, o. X 1,780.

B. 50 days after hatching. Steroid producing cells near centre. Oocyte, a. X 1,700.

Figure 1.19: Steroid-producing cells are described in the ovary of tilapia Sarotherodon niloticus during ovarian differentiation. As the ovarian cavity is forming, these cells appear near the blood vessels of the stroma on the side facing the mesentery. These photomicrographs of cross sections of the ovary show many steroid-producing cells near the blood vessels. (From Naka-mura and Nagahama, 1985; reproduced with permission from Blackwell Publishing).

A. 35 days after hatching. Sterioid producing cells at centre left. Premeiotic oocyte, o. X 1,780.

B. 50 days after hatching. Steroid producing cells near centre. Oocyte, a. X 1,700.

Figure 1.20: Steroid-producing cells are presumed to originate from stromal elements and, as the ovary develops, their numbers increase surrounding the blood vessels. This electron micrograph of a section of a steroid-producing cell from the ovary of tilapia Sarotherodon niloticus 50 days after hatching shows the tubular mitochondrial cristae and tubular agranular endoplasmic reticulum which are characteristic of steroid production. X 25,000 (From Nakamura and Nagahama, 1985; reproduced with permission from Blackwell Publishing).

Figure 1.21: Photomicrographs of cross sections of the gonad of developing tilapia Sarotherodon niloticus. It is suggested that the steroids produced by steroid-producing cells play a role in the formation of the ovarian lumen and in the differentiation of germ cells. (From Nakamura and Nagahama, 1985; reproduced with permission from Blackwell Publishing).

A. Indifferent gonad 17 days after hatching. A germ cell (g) is surrounded by a few stromal cells. X 1,240.

B. Ovary 26 days after hatching. Steroid-producing cells are seen near the blood vessels. Stromal aggregations (sa large arrow) in the proximal and distal region represent the initial formation of the ovarian cavity. Germ cells are not seen. X 940.

C. Ovary 30 days after hatching showing stromal aggregations (large arrows), cysts containing oogonia and oocytes (o), and steroid-producing cells (small arrows). X 560.

D. Ovary 50 days after hatching showing several oocytes (a) in the perinucleolus stage and numerous steroid-producing cells near blood vessels (arrows). Ovarian cavity, oc. X 340.

Figure 1.21: Photomicrographs of cross sections of the gonad of developing tilapia Sarotherodon niloticus. It is suggested that the steroids produced by steroid-producing cells play a role in the formation of the ovarian lumen and in the differentiation of germ cells. (From Nakamura and Nagahama, 1985; reproduced with permission from Blackwell Publishing).

A. Indifferent gonad 17 days after hatching. A germ cell (g) is surrounded by a few stromal cells. X 1,240.

B. Ovary 26 days after hatching. Steroid-producing cells are seen near the blood vessels. Stromal aggregations (sa large arrow) in the proximal and distal region represent the initial formation of the ovarian cavity. Germ cells are not seen. X 940.

C. Ovary 30 days after hatching showing stromal aggregations (large arrows), cysts containing oogonia and oocytes (o), and steroid-producing cells (small arrows). X 560.

D. Ovary 50 days after hatching showing several oocytes (a) in the perinucleolus stage and numerous steroid-producing cells near blood vessels (arrows). Ovarian cavity, oc. X 340.

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Responses

  • giuliano
    How do you find eel gonads?
    6 years ago

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