G

Figure 1.22: In many teleosts, the visceral peritoneum covering the ovary and the peritoneum lining its cavity often continue posteriorly, beyond the mass of ovarian tissue, to form the unique oviduct. This extension of the ovarian cavity continues posteriorly to connect with the genital pore leading to the exterior. (After Giersberg and Rietschel, 1968).

Abbreviations: G, genital pore; O, oviduct; Pp, parietal peritoneum lining ovarian cavity; Pv, visceral peritoneum covering ovary.

Figure 1.22: In many teleosts, the visceral peritoneum covering the ovary and the peritoneum lining its cavity often continue posteriorly, beyond the mass of ovarian tissue, to form the unique oviduct. This extension of the ovarian cavity continues posteriorly to connect with the genital pore leading to the exterior. (After Giersberg and Rietschel, 1968).

Abbreviations: G, genital pore; O, oviduct; Pp, parietal peritoneum lining ovarian cavity; Pv, visceral peritoneum covering ovary.

Figure 1.23: Photomicrograph of a section of the ovary of a sexually mature goldfish Carassius auratus. The vertebrate ovary is an aggregation of developing follicles enmeshed in a vascular stroma of loose connective tissue and enclosed within an envelope of gonadal epithelium. The stroma consists of collagenous, elastic, and reticular fibres and becomes greatly distended as the follicles enlarge. The clear spaces in the stroma are the result of inevitable shrinkage. X 400 (From Cotelli et al., 1988; reproduced with permission from Elsevier Science). Abbreviations: a, previtellogenic oocytes; b, vitellogenic oocyte.

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Figure 1.24: Beneath the ovarian envelope, a condensation of stromal tissue forms the capsule or tunica albuginea. This electron micrograph of the well developed capsule of the ovary of Fundulus heteroclitus shows abundant collagen (C) and smooth muscle (SM). Inner epithelioid cells (ES) of the stroma line the stromal space (SP). X 7,000 (From Brummett, Dumont, and Larkin, 1982; © reproduced with permission of John Wiley & Sons, Inc.).

Figure 1.24: Beneath the ovarian envelope, a condensation of stromal tissue forms the capsule or tunica albuginea. This electron micrograph of the well developed capsule of the ovary of Fundulus heteroclitus shows abundant collagen (C) and smooth muscle (SM). Inner epithelioid cells (ES) of the stroma line the stromal space (SP). X 7,000 (From Brummett, Dumont, and Larkin, 1982; © reproduced with permission of John Wiley & Sons, Inc.).

Figure 1.25: Photomicrograph of a section of an ovarian follicle of the brook stickleback Eucalia inconstans stained with silver to show the "basket" of reticular fibres surrounding an early oocyte. X 480 (From Braekevelt and McMillan, 1967; © reproduced with permission of John Wiley & Sons, Inc.).

Figure 1.25: Photomicrograph of a section of an ovarian follicle of the brook stickleback Eucalia inconstans stained with silver to show the "basket" of reticular fibres surrounding an early oocyte. X 480 (From Braekevelt and McMillan, 1967; © reproduced with permission of John Wiley & Sons, Inc.).

Figure 1.26: Early follicles consist of primordial germ cells, newly arrived by migration, enclosed within a cluster of follicular cells derived from divisions of the gonadal epithelial cells. Primordial germ cells in the ovary of the eel Anguilla anguilla divide by mitosis to produce diploid oo-gonia. One germ cell is in metaphase (mPGC), another is in prophase (pPGC). Electron micrograph X 3,000 (From Grandi and Colombo, 1997; © reproduced with permission of John Wiley & Sons, Inc.).

Abbreviations: ch, Chromosomes; cf, bundle of collagen fibrils; dPGC, degenerating germ cell; GPE, gonadal peritoneal epithelium; PGC-2, secondary primordial germ cell.

Figure 1.27: Oogonia form diploid primary oocytes by mitotic division. Meiotic division of a primary oocyte in the ovary results in a secondary oocyte and first polar body, both diploid. This section of the ovary of the eel Anguilla anguilla shows a cyst of synchronized meiotic oocytes in the zygotene stage, all connected by cytoplasmic bridges (IB). The cyst is enveloped by flattened somatic cells (SC) and is separated by a basal lamina (BL) from the stroma. The oocyte nuclei contain a nucleolus (nu) and synaptonemal complexes (Syc) with chromatin attached to the lateral elements. GPE, gonadic peritoneal epithelium. Electron micrograph X 34,400 (From Grandi and Colombo, 1997; © reproduced with permission of John Wiley & Sons, Inc.).

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Figure 1.28: Some epithelial cells, whose processes envelop meiotic oocytes, transform into prefollicular cells which become follicular cells at the completion of folliculogenesis. Electron micrographs of the ovary of the common snook Centropo-mus unidecimalis. (From Grier, 2000; © reproduced with permission of John Wiley & Sons, Inc.).

A. The stratified germinal epithelium extends between the ovarian lumen (OL) and the basement membrane (arrowheads) and is composed of epithelial cells (E), a cell nest of meiotic oocytes (in the pachytene stage), and a diplotene oocyte (DO) near the basement membrane. Pachytene oocytes have synaptonemal complexes (s), nucleoli (nu), perhaps multiple nucleoli (arrows), prominent Golgi bodies (g), and nuage (n) surrounded by mitochondria. The single oocyte in diplotene (DO) is being encompassed by prefollicular cells (PF) with pleomorphic nuclei (*). Newly formed diplotene oocytes have a prominent nucleolus and lack basophilic cytoplasm. The extravascular space (EVS) is nearly occluded by prethecal cells (PT) and a capillary is observed with a single red blood cell (RBC). A nest of oocytes (ON) is seen at the lower left. Bar = 2 pm.

B. Epithelial cells of the germinal epithelium (E) border the ovarian lumen (OL) and encompass an oocyte (OE), isolating it from the lumen. Oocytes with basophilic cytoplasm (OB) and oocytes without (O) are contained within a cell nest still attached to the germinal epithelium. The basement membrane (BM) is continuous over the surface of the nest and also the base of the germinal epithelium (arrows). Prethecal cells (PT) lie within the interstitium. Nuage (n) is present in the smaller oocytes. In the nucleus of a larger oocyte with basophilic cytoplasm, granular material denoting RNA synthesis (arrowhead) is present between the nucleolus and nuclear membrane; the nucleus is ringed by mitochondria (m). These oocytes are not yet enclosed within a follicle although prefollicular cells (*) may completely encompass them. Bar = 1 |im.

Figure 1.28: Continued.

C. Upper left. A portion of an oocyte nest. One diplotene oocyte with basophilic cytoplasm (OB), surrounded by prefollicular cells (PF) is becoming a follicle. Prefollicular cells also surround the nest where oocytes (O) are in contact with each other. These oocytes display prominent nucleoli (nu), vesicular mitochondria (m), and Golgi bodies (g). A prethecal cell (PT) lies between the basement membranes of the forming follicle and cell nest. Bar = 1 |im. Upper right. An enlargement of the prethecal cell (PT). The basement membrane extends between the layers of follicular cells (F) that surround the oocyte (O) and the prefollicular cells (PF) around the oocyte nest. Processes from the prethecal cells do not penetrate between these basement membranes (arrowheads). Bar = 1.75 |im. Lower. Portions of three follicles, each containing a basophilic oocyte (OB) encompassed by follicular cells (F). Basement membranes (arrows) separate the follicles from the theca interna. EVS, extravascular space. Bar=l |im.

Figure 1.28: Continued.

C. Upper left. A portion of an oocyte nest. One diplotene oocyte with basophilic cytoplasm (OB), surrounded by prefollicular cells (PF) is becoming a follicle. Prefollicular cells also surround the nest where oocytes (O) are in contact with each other. These oocytes display prominent nucleoli (nu), vesicular mitochondria (m), and Golgi bodies (g). A prethecal cell (PT) lies between the basement membranes of the forming follicle and cell nest. Bar = 1 |im. Upper right. An enlargement of the prethecal cell (PT). The basement membrane extends between the layers of follicular cells (F) that surround the oocyte (O) and the prefollicular cells (PF) around the oocyte nest. Processes from the prethecal cells do not penetrate between these basement membranes (arrowheads). Bar = 1.75 |im. Lower. Portions of three follicles, each containing a basophilic oocyte (OB) encompassed by follicular cells (F). Basement membranes (arrows) separate the follicles from the theca interna. EVS, extravascular space. Bar=l |im.

in the suiTounding thecal cells. X 4,500.

D. Electron micrograph of an intercellular bridge (arrow) between two oocytes. The membranes bordering the bridge are electron dense and about 30 nm in thickness. X 9,000.

E. Electron micrograph of a primary follicle in the ovary of a neonate. The diplotene oocyte is surrounded by a single layer of squamous follicular cells. X 3,000.

Abbreviations: BL, basal lamina; ER, granular endoplasmic reticulum; FC, follicular cells; L, liposomes; M, mitochondria; N, nucleus; Nu, nucleolus; SC, thecal cells.

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Figure 1.30: Division of developing germ cells in the ovaries of lampreys Petromyzon marinus causes evaginations of the ovarian wall to expand ventrally, subdividing the ovary into lobes and lobules that contain a stroma of vascular connective tissue. (From Lewis and McMillan, 1965; © reproduced with permission of John Wiley & Sons, Inc.).

A, B,C. (A) Three cell nests are surrounded by peritoneum and penetrated by a stroma of vascular connective tissue. (B) Each of these cell nests gives rise to a group of cell nests, each of which constitutes a lobe of the ovary; the vascular stroma has penetrated between the cell nests. (C) As division continues, the progeny of each cell nests forms a lobule; the lobule is a discrete group of oocytes (o), roughly two cells in thickness, contained within peritoneum. CN, cell nest; P, peritoneum; S, stroma. D. Photomicrograph of a section of the ovary of an ammocoete in early metamorphosis showing the ovigerous folds which are flat, leaf-like extensions of ovarian tissue. X 45.

Figure 1.30: Division of developing germ cells in the ovaries of lampreys Petromyzon marinus causes evaginations of the ovarian wall to expand ventrally, subdividing the ovary into lobes and lobules that contain a stroma of vascular connective tissue. (From Lewis and McMillan, 1965; © reproduced with permission of John Wiley & Sons, Inc.).

A, B,C. (A) Three cell nests are surrounded by peritoneum and penetrated by a stroma of vascular connective tissue. (B) Each of these cell nests gives rise to a group of cell nests, each of which constitutes a lobe of the ovary; the vascular stroma has penetrated between the cell nests. (C) As division continues, the progeny of each cell nests forms a lobule; the lobule is a discrete group of oocytes (o), roughly two cells in thickness, contained within peritoneum. CN, cell nest; P, peritoneum; S, stroma. D. Photomicrograph of a section of the ovary of an ammocoete in early metamorphosis showing the ovigerous folds which are flat, leaf-like extensions of ovarian tissue. X 45.

Figure 1.31: The ovary of the hagfish Myxine glutinosa forms a dorsal, narrow ribbon suspended from the mesovarium in the midline. (Figures A and G are from Walvig, 1963; reproduced with permission. B to F are from Patzner, 1974, and are reproduced, with permission, from the Norwegian Journal of Zoology).

A. The ovary (O) consists of "series" of follicles that develop from oogonia contained within a band of germinal cells that runs along the free edge of the ovary (GE). The movement of oocytes and follicles as well as follicular involution is indicated in this imaginary diagram. Maturing oocytes (1) move from the band of germinal cells into the vascular connective tissue of the inner part of the ovary (2 to 5). Undifferentiated squamous mesothelial cells attach to the oocytes and stretch to enclose them within a follicular epithelium. Four "generations" of oocytes are shown, developing from oogonia in the germinal band (I to IV); they grow to a diameter of 1 to 2 mm whereupon they enter a resting period awaiting ovulation of the previous generation of oocytes. After the mature egg (6) is ovulated, the empty follicle (7) forms a postovulatory corpus luteum (PO) that regresses as it moves toward the mesovarium (MO) (8 to 11). Some follicles undergo atresia at some point in their development (PR).

C. An enlarged portion of B showing the oogonia (Og) in the germinal band and oocytes (Oc) within the ovary. X 600.

Figure 1.31: The ovary of the hagfish Myxine glutinosa forms a dorsal, narrow ribbon suspended from the mesovarium in the midline. (Figures A and G are from Walvig, 1963; reproduced with permission. B to F are from Patzner, 1974, and are reproduced, with permission, from the Norwegian Journal of Zoology).

A. The ovary (O) consists of "series" of follicles that develop from oogonia contained within a band of germinal cells that runs along the free edge of the ovary (GE). The movement of oocytes and follicles as well as follicular involution is indicated in this imaginary diagram. Maturing oocytes (1) move from the band of germinal cells into the vascular connective tissue of the inner part of the ovary (2 to 5). Undifferentiated squamous mesothelial cells attach to the oocytes and stretch to enclose them within a follicular epithelium. Four "generations" of oocytes are shown, developing from oogonia in the germinal band (I to IV); they grow to a diameter of 1 to 2 mm whereupon they enter a resting period awaiting ovulation of the previous generation of oocytes. After the mature egg (6) is ovulated, the empty follicle (7) forms a postovulatory corpus luteum (PO) that regresses as it moves toward the mesovarium (MO) (8 to 11). Some follicles undergo atresia at some point in their development (PR).

C. An enlarged portion of B showing the oogonia (Og) in the germinal band and oocytes (Oc) within the ovary. X 600.

Figure 1.31: Continued.

B. Photomicrograph of a section through the gonad of a 15-cm female. X 290. Oogonia originate in the band of germinal cells (Ke) and migrate to the vascular connective tissue of the inner part of the ovary where they under go meiotic division to become oocytes (Oh).

Abbreviations: D, intestinal epithelium; Ke, germinal cells; M, mesentery; MI, mesovarium; N, nerve; Oh, oocytes; Vs, supra-intestinal vein.

Figure 1.31: Continued.

B. Photomicrograph of a section through the gonad of a 15-cm female. X 290. Oogonia originate in the band of germinal cells (Ke) and migrate to the vascular connective tissue of the inner part of the ovary where they under go meiotic division to become oocytes (Oh).

Abbreviations: D, intestinal epithelium; Ke, germinal cells; M, mesentery; MI, mesovarium; N, nerve; Oh, oocytes; Vs, supra-intestinal vein.

Figure 1.31: Continued.

D. Electron micrograph of a section through the germinal band of a 14-cm female showing two oogonia (K) and one germinal cell. Collagenous fibres (Kf) provide support in the vascular stroma. The basal lamina (Bm) is shown. Arrows indicate undulations of the outer nuclear membrane of an oogonium. X 14,300.

Figure 1.31: Continued.

E. Electron micrograph of a portion of a primary follicle, showing the thin follicular epithelium (F) surrounding an oocyte (Cy). A thecal cell (T) is supported by collagenous fibres (Kf). A peritoneal cell (P) of the mesothelium encloses the ovary. Bm, basementmembrane. X 14,200.

Figure 1.31: Continued.

E. Electron micrograph of a portion of a primary follicle, showing the thin follicular epithelium (F) surrounding an oocyte (Cy). A thecal cell (T) is supported by collagenous fibres (Kf). A peritoneal cell (P) of the mesothelium encloses the ovary. Bm, basementmembrane. X 14,200.

Figure 1.31: Continued.

F. Electron micrograph of a portion of a maturing follicle approximately 100 |im in diameter. An oocyte (Cy) is enclosed by a squamous follicular cell (F) resting on its basement membrane. The theca consists of flattened thecal cells (T) and stout collagenous fibres (Kf). A peritoneal cell (P) of the mesothelium rests on its basement membrane (Bm). X 24,000.

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