2I 4 



UROGENITAL SYSTEM 



Hind-gut 



Mesonephric 

 ducf 



Allaniois 

 Cloaca. 



I Cloacal membrane 



'l/anfois 



'loacai membrane 



Hind-qui 



Mesoncphri 

 duct 



Mctiui* 



Cloaca. 



Mesonephric duct 

 AllantoLS 



Metanephros 



"loacal mtmlrane \= 



Cloaca. 



Tail-gut 



Cloacal r 



membrane 



FIG. 209. Four stages showing the differentiation of the cloaca into the rectum, urethra and blad- 

 der. A, from an embryo of 3.5 mm.; B, a somewhat later stage; C, from a 5 mm. embryo; D, from an 

 embryo of 7 mm. (after reconstructions by Pohlman). About 100 diameters. 



Mesonephric. duct 

 Metanephros 



Intestine 



Allan foil 



Anlage of bladder 



Ureter 



Cloacal 

 membrane 



Uroqenifal sinus 

 nee turn 



FlG. 210. Reconstructions from a 12 mm. embryo showing the partial subdivision of the cloaca into 

 rectum and urogenital sinus (after Pohlman). 



