. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative. THE DEVELOPMENT OP THE EMBflYO ITSELF. 117 In both sexes the most posterior portion of the Wolffian duct gives rise to the metanephros, or what becomes the permanent kidney and m-eter ; in the male also to the vas deferens, testicle, vas aberrans, and seminal vesicle. The ovary has a similar origin to the testicle ; the germinal epithelium furnishing the cells, which are transformed into Graafian follicles, ova, etc., and the mesoblast the stroma in which these
. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative. THE DEVELOPMENT OP THE EMBflYO ITSELF. 117 In both sexes the most posterior portion of the Wolffian duct gives rise to the metanephros, or what becomes the permanent kidney and m-eter ; in the male also to the vas deferens, testicle, vas aberrans, and seminal vesicle. The ovary has a similar origin to the testicle ; the germinal epithelium furnishing the cells, which are transformed into Graafian follicles, ova, etc., and the mesoblast the stroma in which these structures are imbedded. In the female the parovarium remains as the representative of the atrophied Wolffian body and duct. The bladder and urachus are both remnants of the formerly extensive allautois. The final forms of the genito-urinary or- gans arise by differentiation, fusion, and atrophy : thus, the cloaca or common cavity of the genito-urinary ducts is divided. AL. ^- CLi Via. 126. Fig. 187. Pig. 128. Fig. 129. Figs. 186 to 189.—Diagrams illustrating the evolution of the posterior passages (after Landois and Stirling). Pig. 126.—AUantois continuous with rectom. Fig. 127.—Cloaca formed. Fig. 188.—Early condition in male, before the closure of the folds of the groove on the posterior side of the penis. Pig. 129.—Early female condition. .A, commencement of proctodseum; .4iiii, allantois; i?, bladder; C, penis; CX, cloaca; M, MflUerian duct; B, rectum; U, urethra; S, vestibule; SU, urogenital sinus; Y, vas deferens in Fig. 188, vagina in Fig. 139. by a septum (the perineum externally) into a genito-urinary and an intestinal (anal) part; the penis in the male and the corresponding clitoris in the female appear in the region of the cloaca, as outgrowths which are followed by extension of folds of integument that become the scrotum in the one sex and the labia in the other. The urethra arises as a groove in the under surface of the. Please note that these images are
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