448 



COMPARATIVE ANATOMY 



FIG. 339. A SERIES or DIAGRAMMATIC FIGURES ILLUSTRATING THE ACCOUNT 

 OF THE COMPARATIVE MORPHOLOGY OF THE URINOGENITAL ORGANS OF THE 

 VERTEBRATA GIVEN IN THE FOLLOWING PAGES. 



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

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



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



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

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

 of female Amniota. 



al, rectum ; al', al", allantois or urinary bladder ; cl, cloaca ; d.m, Miillerian duct, 

 which in Mammals becomes differentiated (Fig. H) into the Fallopian tube 

 (/), the uterus (ut), and the vagina (vg) ; d.ms, duct of the mesonephros, 

 which in male Amphibians and Elasmobranchs becomes (Fig. C) the urino- 

 genital, 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) ; d.pn., duct of the pronephros ; g.c, Cowper's glands ; g.g, gonads, 

 undifferentiated stage ; hy, and u.m (Fig. G), xinstalked hydatids and uterus 

 masculinus (vestiges, in the male, of the Miillerian duct, d.m) ; hy.s, stalked 

 hydatid ; ms, the developing mesonephros ; ms.r, renal portion of meso- 

 nephros ; ms. s, part of the mesonephros becoming converted into the epidi- 

 dymis and parovarium ; ms.v, vestiges of the mesonephros (paradidymis and 

 paroophoron) ; m.t, the definitive kidney or metanephros of the Amniota ; os, 

 abdominal aperture of oviduct ; ov, ovary ; p.a, abdominal pore ; p.g, penis, 

 clitoris ; p.n, pronephros ; su, urinogenital sinus ; ts, testis ; ur, ureter ; v.s, 

 seminal vesicle, an outgrowth of the duct of the mesonephros ; t> rete and 

 vasa efferentia testis ; ft, a network homologous with these structures at 

 the hilum of the ovary. 



TABULATED RESUME OF THE FACTS PICTORIALLY ILLUSTRATED ON PAGE 447. 



^ a 



Anunniin. 



Develops in all Anamnia, but 

 rarely persists as a permanent 

 excretory organ. 



In Elasmobranchs and some 

 Amphibians appears to give 

 origin by subdivision to the 

 mesonephric (Wolffian) and 

 Miillerian ducts. In other 

 Amphibia, becomes converted 

 into the mesonephric duct. Its 

 fate in other Anamnia is not yet 

 fully investigated. 



Amniota. 



Still develops in the Amniota, 

 but as an excretory organ under- 

 goes entire degeneration in the 

 embryo. 



Persists as the mesonephric 

 (Wolffian) duct, and contributes 

 to some extent in the formation 

 of the Miillerian duct. 



Serves 

 urinary 



in all Anamnia as a 

 gland. In Plagio- 

 stomes, Ganoids, Dipnoans, 

 and Amphibians, a certain por- 

 tion becomes related to the male 

 genital apparatus, the remaining 

 portion persisting as a permanent 

 kidney. 



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 genital 

 apparatus in the male. 



