GENERATION OF ANIMALS, I. xiii. 



nature that the residue from the fluid nourishment 

 shares the use of the same passage. This is clear 

 from the fact that although all animals produce 

 semen, fluid residue is not formed in all of them. 



Now in males the seminal passages must have a 

 fixed position and not stray about, and the same is 

 true of the uterus in females ; and this fixed position 

 must of necessity be either towards the front or the 

 back of the body. Hence, (a) in the \'i\ipara the 

 uterus is in front, on account of the embryo ; (6) in 

 the Ovipara it is by the loin and at the back ; (c) in 

 those animals which begin bv producing eggs within 

 themselves and later bring their young forth exter- 

 nally, both positions are found combined, because 

 the animals share the characteristics of both classes ; 

 they are viviparous and oviparous ahke ; thus, the 

 upper portion of the uterus, in which the eggs are 

 formed, is below the diaphragm by the loin, and 

 towards the back ; but its continuation is lower 

 down, by the abdomen, for from this point onwards 

 the production of live young begins. In these 

 animals also there is one passage only for the solid 

 residue and for copulation ; none of them has a 

 pudendum projecting from the body, as has been 

 said before. What is true of the uterus in Ovipara 

 is true also of the passages in the males, both those 

 which have testes and those which have not. In all 

 of them the passages are fastened towards the back 

 near the region of the spine ; fastened, because 

 they may not stray about, but must have a settled 

 position, which is just what the back part of the 

 body provides ; it gives continuity and stability. 

 Indeed, in those animals which have their testes 

 inside, the passages acquire their fixed position at 



41 



