REPRODUCTION 195 



up with a new duct opening into the cloaca. Thus there arises from 

 the female urinary system a pair of entirely distinct oviducts. An 

 egg, liberated from the ovary into the coelom, finds its way into 

 one of the oviducts and descends directly to the outside, or into an 

 enlargement (uterus) of the terminal portion of the duct where 

 development proceeds until birth occurs. (Figs. 129, D; 132.) 



The female reproductive system, though derived from the 

 mesonephric system, has become entirely independent of it. Ac- 

 cordingly the disappearance of the mesonephros and duct in higher 

 Vertebrates, when it is replaced by the metanephros and the ureter 

 as the functional urinary system, has little effect on the female 

 reproductive system. As a matter of fact, the abandoned meso- 

 nephros and duct degenerate and disappear in the female, while 

 in the male the mesonephric duct remains and becomes completely 

 appropriated by the reproductive system. The sperm now pass 

 directly into the former mesonephric duct, which thereby becomes 

 solely a sperm duct. (Fig. 129, E, F.) 



Such is the historical origin of the foundations of the reproduc- 

 tive system as it occurs in the Reptiles, Birds, and Mammals. 

 Each of these groups, building on this foundation, has developed 

 modifications and additions demanded by its special lines of evolu- 

 tion. It appears again that, whenever possible, structures at hand 

 are employed to construct what is to be, and thus is woven in the 

 woof and warp of higher forms a partial record of their ancestry. 

 (Fig. 134B.) 



