GENERATION OF ANIMALS, I. ii.-in. 



underg6 an accompanying change." This is clear 

 with castrated animals, where, although the genera- 

 tive part alone is destroyed, almost the whole form 

 of the animal thereupon changes so much that it 

 appears to be female or very nearly so, which 

 suggests that it is not merely in respect of some 

 casual part or some casual faculty that an animal is 

 male or female. It is clear, then, that " the male." 

 and " the female " are a principle. At any rate, 

 when apimals undergo a change in respect of that 

 wherein they are male and female, many other things 

 about them undergo an accompanying change, which 

 suggests that a principle undergoes some alteration. 



The testicles and the uterus are not of similar III 

 arrangement in all the blooded animals. Consider 

 first the males, and their testicles. Some blooded 

 animals (as the groups of Irishes and Serpents) have 

 no testicles at all, only two seminal passages. ° Others 

 have testicles, but they are inside, by the loin, near 

 the place where the kidneys are ; from each of them 

 runs a passage (as in those animals which have no 

 testicles), and these two passages join up together 

 (again like those other animals) : among the class 

 of animals which breathe air and have a lung, this 

 occurs in all the Birds and in the o\'iparous quadru- 

 peds, for all these as well have their testicles inside, 

 by the loin, and two passages leading from them, just 

 as the Serpents have : examples are the lizards, the 

 tortoises, and all the animals with homy scales. All 



sex hormones from the interstitial cells of the testis and ovary 

 respectively. 



* These are in fact the testes, but Aristotle reserves this 

 name for the firm, oval-shaped testes. This negative state- 

 ment does not of course include the cartilaginous fishes, the 

 Selachia, many of which are viviparous. 



15 



