GENERATION OF ANIMALS, IV. v. 



since this also is a condition due to there being 

 no evacuation (which corresponds to the emission of 

 semen in the male), and mares discharge extremely 

 Uttle evacuation. Further, in all the \ivipara those 

 females which are barren are prone to sexual in- 

 tercourse, because they are in a similar condition 

 to males when their semen is ready, collected 

 together," but is not being emitted, the evacuation 

 of the menstrual fluid in females being the emission 

 of semen, since, as has been stated earlier, the 

 menstrual fluid is semen that is unconcocted. 

 Hence, too, those women who are incontinent 

 in the matter of sexual intercourse, cease from 

 their passionate excitement when they have borne 

 several children, because once the seminal residue 

 has been expelled from the body it no longer pro- 

 duces the desire for this intercourse. Among birds 

 the females are less sexually excitable than the males 

 because their uterus is close up by the diaphragm, 

 whereas the males, on the contrary, have their testes 

 drawn up internally,* so that if any class of such 

 creatures tends naturally to abound in semen, they 

 are always wanting to have sexual intercourse. Thus 

 in females it is the descent of the uterus which 

 encourages copulation, whereas in males it is the 

 dra>Wng up of the testicles. 



We have now stated the cause on account of which 

 superfetation does not occur at all in some animals, 

 why it does occur in others, and why these can some- 

 times bring the nourishing of the fetation to comple- 

 tion, sometimes not ; and what is the cause why of 

 such animals some are prone to sexual intercourse 

 and others not. 



» Cf. in b 25, 718 a 6 flF. * See 717 b 10 ff. 



451 



