. Comparative anatomy. Anatomy, Comparative. THE UROGENITAL SYSTEM 411 and the abdominal pores open posteriorly into the urogenital sinus and to the outside through a urogenital papilla. Elasmobranchs. The gonads of elasmobranchs are paired, and in some species greatly elongated, especially in the male. The testes acquire secondary connexions with the anterior part of the mesonephros, and use the mesonephric ducts as an outlet for the sperm. Elasmobranchs retain abdominal pores, but they appear to be functionless. In this group, the primitive pronephric duct splits longitudinally to form Wolff
. Comparative anatomy. Anatomy, Comparative. THE UROGENITAL SYSTEM 411 and the abdominal pores open posteriorly into the urogenital sinus and to the outside through a urogenital papilla. Elasmobranchs. The gonads of elasmobranchs are paired, and in some species greatly elongated, especially in the male. The testes acquire secondary connexions with the anterior part of the mesonephros, and use the mesonephric ducts as an outlet for the sperm. Elasmobranchs retain abdominal pores, but they appear to be functionless. In this group, the primitive pronephric duct splits longitudinally to form Wolffian and Muellerian ducts. In the female the Wolffian ducts are purely OVARIAN OVUM DEGENERATING OVUM. .-fby®5^j^0 SPERMATOZOA INTERSTITIAL TISSUE HISTOGENESIS OF TESTIS - RANA. PORTION OF SECTION C-C MUCH ENLARGED. Fig. 338.—An enlarged portion of a section of the posterior lobule shown in 337, A. The ovarian sacs are being changed into crypts containing spermatozoa, degenerating sac on the left spermatozoa have already made their appearance. Fig. In a excretory, while the Muellerian ducts form the oviducts. In the male, the Wolffian ducts combine both urinary and reproductive functions, while Mueller's ducts atrophy to form the uterus masculinus. Many elasmo- branchs are viviparous, and the eggs are retained until hatched within uterus-like enlargements of the oviducts. In some species, the embryonic yolk-sac, which is richly supplied with blood-vessels, unites with the wall of the oviduct to form a yolk-sac placenta. Amphibia. The gonads of amphibia resemble those of elasmobranchs. As in the latter, the testis becomes connected by means of vasa efferentia with anterior tubules of the mesonephros, and this part of the mesonephros tends to atrophy and lose its excretory function. The Wolffian duct serves as a urogenital outlet in the male. The Muellerian ducts, which persist as rudiments in the male, become the oviducts of the Please note that these images are extra
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