GENERATION OF ANIMALS, IV. v. 



discharged is more than sufficient, and this when 

 divided up into portions causes the production of 

 numerous offspring, one of which is later than another. 

 When, however, the fetation is already advanced in 

 its growth before the copulation takes place, super- 

 fetation sometimes occurs, but infrequently, because 

 in women tRe uterus generally closes up during the 

 time of pregnancy. But if ever it does happen (as in 

 fact it has been known to do), the mother cannot 

 bring the second one to completion, but ejects feta- 

 tions that are very similar to what are known as 

 abortions. The situation is comparable with that in 

 the one-offspring animals, in which, on account of 

 their size, all the residue is directed to the already 

 existing embryo. So too it happens in these animals,'' 

 except that in the former it happens straight away, 

 whereas in these it happens when the embryo is 

 already advanced in growth, because then their con- 

 dition is similar to that of the one-offspring animals. 

 Similarly, because man is by nature an animal which 

 produces numerous offspring, and because there is 

 something over and to spare as regards the size both 

 of the uterus and of the residue (though not enough 

 to bring the nourishing of a second embrvo to com- 

 pletion), women and mares are the only animals which 

 admit copulation while they are with young. In 

 women it is due to the reason already stated ; in 

 mares it is due to the barrenness of their nature,^ 

 and because the size of their uterus has something 

 over and to spare — there is more than enough room 

 for one, but not sufficient for a second fetation to be 

 brought to completion. Also, mares are by nature 

 prone to sexual intercourse because they are in the 

 same predicament as females which are barren — 



Q 44.9 



