. The biology of the amphibia. Amphibians. THE UROGENITAL SYSTEM 281 arise from the anterior part of the developing gonad, although this has been denied by some investigators (Kennel, 1913). They reach their maximum size in the fall before hibernation and their minimum size after egg laying. Partial castration causes the fat bodies to hypertrophy (Dubois, 1927). Removal of the fat bodies causes a degeneration of the sexual products, the most advanced stages degenerating first (Adams and Rae, 1929). The fat bodies are therefore necessary for maintaining the health and normal development of the
. The biology of the amphibia. Amphibians. THE UROGENITAL SYSTEM 281 arise from the anterior part of the developing gonad, although this has been denied by some investigators (Kennel, 1913). They reach their maximum size in the fall before hibernation and their minimum size after egg laying. Partial castration causes the fat bodies to hypertrophy (Dubois, 1927). Removal of the fat bodies causes a degeneration of the sexual products, the most advanced stages degenerating first (Adams and Rae, 1929). The fat bodies are therefore necessary for maintaining the health and normal development of the gonads. Ovulation.—The eggs lie in the cortex of the ovary and each egg during the growth period is surrounded by a layer of follicle cells which is enclosed by a vascular network. A thin vitelline membrane covers the surface of the mature egg. This membrane is duplex, an outer portion, the zona pellucida, having been produced by the follicle cells (Fig. 102) and an inner portion, the zona radi- ata, by the egg itself. The eggs project into the lumen of the ovary, and the outer surface of the latter is covered with peritoneum. During the breeding season each egg breaks through the wall of the ovary at the point where its stalk joins the ovarian epithelium. A small hole ap- pears in the peritoneum and the egg in squeezing through this aperture may be forced into an hourglass shape (Smith, 1916). The egg when free in the peritoneal cavity is said to be carried to the open mouths of the Miillerian ducts by ciliary action. Smith (1916) finds few cilia present in either Rana pipiens or Cryptobranchus, however, and it seems possible that eggs are forced into the oviducts partly by suction; the mouths of the oviducts being attached to the pericardium would gape open at each heart beat. The movements of the female would also tend to squeeze the eggs through the outlet. Fertilization in some salamanders takes place near the mouth of the oviduct, the egg having thrown off the polar bod
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Keywords: ., bookcentury1900, bookpublishernewyorkmcgr, booksubjectamphibians
