PHYLOGENY OF URINARY AND SEXUAL OROANa 429 



TI. Sixth Period : Oenitals amd Kidney $ of Cyclostom: 



G.. The seraal glands (nomerons in Acrania) coalesce into a p&ir. 



U. The primitive kidney ducts send out lateral branches which acquire 

 rascular ooils (glomeruli) (the semi-pinnate primitiye kidneys of BdeUo- 

 stomtk). 



XLIII. B. Second main diyision : the genital organs (G) and tiie vrixuurj 

 organs (U) become united. (The sexual system and the urinary system 

 are united in the " urogenital system.") 



VII. Seventh Period : Urogenitals of Primitive Pishes (SeUiehii). 



The primary primitive kidney duct differentiates on each side, f(wrming 

 two secondary canals ; the Wolffian duct, which develops into the seed-duct, 

 and the Miillerian duct, which develops into the oviduct. Both genital 

 doots originally open behind the anus (JProselachii). 



VIII. Eighth Period : Urogenitals of Dipneusta, 



A cloaca is formed by the union of the urogenital opening and the cavity 

 of the anus. The single urinary bladder grows out from the anterior wall of 

 the rectum (Lepidosiren). 



IX. Ninth Period : Urogenitals of Amphibia, 



Prom the uppermost part of the primitive kidney which is in process of 

 atrophy, proceeds, in the male sex, the supplementary testis ; in the female 

 sex, the supplementary ovary. The Wolffian duct yet acts, in both sexes, an 

 a urinary canal, and, in the male, also as the seed-duct. The MiilleriaD 

 duct acts in the female sex as oviduct ; in the male it is a radimentar^ 

 organ (Bathke's duct). 



X. Tenth Period : Urogenitals of ProtamiUm. 



Hie atrophied primitive kidney is replaced by the permanent seoondary 

 kidney as the urinary organ. The urinary bladder grows out from the 

 ventral orifice of the embryo and fuM-ms the allantois. From the anterior 

 wall of the cloaca grows the sexual protuberance (phaUiks), whlok, in the 

 male, develops to the penis, in the female, to the clitoriB. 



I 



XI. Eleventh Period : Urogenitals of MonoWemse* 



Tbe lower end of the oviduct enlarges on each side to % mafcnlar 

 atema. 



XII. Twelfth Period : Urogenitals of lfar«i(piaZ««. 



The cloaca is separated by a partition into an anteri(»: urogenitftl opening 

 %pertura Mrogenitalis) and a posterior anal opening (onta). Fron the 



