THE KTONEY 37 



drained, these ducts emptying, with the intestine, into a 

 common posterior vent or cloaca. But as the kidney built 

 up the archinephric duct, the ovary and testis invaded 

 it as a route of egress for their products, and thereafter 

 the urinary system and the reproductive system became 

 so entangled, especially in the male, that the two sys- 

 tems—excretory and reproductive— were not entirely 

 separated until the reptiles were evolved— to the confu- 

 sion of students of comparative anatomy, who sometimes 

 have difficulty in allocating the proper anatomical and 

 physiological priorities. 



To sum up this confusion as succinctly as possible, 

 the archinephric duct sometimes retains a pure urinary 

 function (hagfish and lampreys); or it may carry both 

 sperm and eggs through nearly all its length (Australian 

 lungfish, sturgeon, gar pike, common frog and mud 

 puppy); or the gonads may take over the anterior part 

 of the duct, leaving the kidney only the posterior part 

 or forcing it to develop a separate duct wholly independ- 

 ent of the archinephric duct— the pattern in the female 

 even within the same species not necessarily conforming 

 with that in the male (sharks and some salamanders); 

 or the kidney may retain the archinephric duct entire 

 while the testis develops its own condxiit (bony fishes); 

 or the kidney may abandon the fight in favor of the 

 testis, when the archinephric duct becomes the sper- 

 matic duct, which carries the sperm from the testis to 

 the seminal vesicles for storage; and in the last case the 

 kidney has to build a new duct entirely of its own— the 

 true ureter as it appears in the reptiles, birds, and 

 mammals. 



The ovary has on the whole been less invasive of the 

 kidney's rights and, with few exceptions, the ova in all 

 vertebrates are virtually thrown free into the body cavity 

 to find their way to the exterior— that is, to the oviduct 

 or uterus— as best they can, by means of open 'peritoneal 

 funnels' (Miillerian ducts or Fallopian tubes). 



The student of anatomy can find solace in the fact 



