UEINOGENITAL ORGANS 



343 



Eici. 273. — A Series of Diacirammatic FiGnRES illustrating the Aocotjnt of 

 THE Comparative Morphology of the Urinogenital Organs or the 

 Veeteerata given in the Following Pages. 



A, the pronephros stage of the Anamnia ; B, a later stage of the same ; C, the 

 urinogenital apparatus of the male Amphibian ; D, the same of the female ; 



E, pronephros stage of the Amniota, the mesonephros as yet rudimentary ; 



F, urinogenital apparatus of the Amniota at a stage at which the sexes are 

 not differentiated ; G, urinogenital apparatus of male Amniota ; H, the same 

 of female Amniota. 



p.7i., pronephros; d.pn., duct of the pronephros; ms., the developing me- 

 sonephros ; ms.s, part of the mesonephros, becoming converted into the 

 epididymis and parovarium ; ms.r, vestiges of the mesonephros, the para- 

 didymis and the paroophoron ; f, rete and vasa efferentia testis ; tt, a 

 network homologous with these structures at the hilum of the ovary ; hy. s, 

 stalked hydatid ; ms. z, portion of the mesonephros which in Amphibians and 

 Elasmobranchs laecomes the so-called pelvic kidney ; d.ins, duct of the 

 mesonephros, which in male Amphibians and Elasmobranchs becomes 

 (Fig. C) the urinogenital, and in females (Fig. D) the urinary duct. In the 

 male Amniota it gives rise to the seminal duct (Fig. G), and in the female to 

 Gartner's duct (Fig. H) ; r.s, the seminal vesicle, an outgrowth of the duct 

 of the mesonephros ; d.m., Milllerian duct, which in Mammals becomes 

 differentiated (Fig. H) into the Fallopian tube [fl ), the uterus (iit), and the 

 vagina [vtj); vs, its abdominal aperture; hy, and u.m (Fig. G), unstalked 

 hydatids and uterus masculinus (vestiges, in the male, of the Miillerian duct, 

 d.m.); m.t., the definitive kidne3' or metanephros of the Amniota, said to 

 arise from the ureter (iir), itself an outgrowth of the mesonephric duct ; al, 

 allantois or urinary bladder ; .111, urinogenital sinus ; jj.ji, genital pi-ominence, 

 <j.g, gonads, undifferentiated stage; ov, ovary; ts., testis; d, cloaca; al, 

 rectum ; p. a, abdominal pore ; rj.c, Cowper's glands. 



Tabulated Resume of the Facts Pictorially Illustrated on the opposite 



Page. 



P-. 





Develops in all Anamnia, but 

 rarelj' persists as » permanent 

 excretory organ. 



In Elasmobranchii, appears to 

 give origin by subdivision to 

 both mesonephric (Wolffian) 

 and Miillerian ducts. In Am- 

 phibia, becomes converted into 

 the mesonephric duct. Its fate in 

 other Anamnia is not yet fully 

 investigated. 



Functions in all Anamnia as a 

 urinary gland. In Elasmo- 

 branchs, Amphibians, and one 

 or two higher Fishes, its anterior 

 portion becomes related to the 

 male genital apparatus, the 

 posterior portion persisting as a 

 permanent kidney. 



Still develops in the Amniota, 

 but as an excretory organ under- 

 goes entire degeneration in the 

 embryo : it may take part in the 

 formation of the suprarenal 

 body (?) 



Probably persists as the meso- 

 nephric (Wolffian) duct, and con- 

 tributes in some to the forma- 

 tion of the Jltlllerian duct. 



Loses its renal function in all 

 Amniota (as a rule in the em- 

 bryo), and becomes vestigial, 

 except so far as it becomes an 

 accessory portion of the repro- 

 ductive apparatus in the male 

 and enters into the formation of 

 the suprarenal body (?) 



