GENERATION OF ANIMALS, I. iii.-iv. 



Insects too the uterus is double, whereas in the 

 smaller ones it is indistinct on account of the small- 

 ness of the creatures' body. 



This describes the arrangement of those parts of 

 animals which I have mentioned. 



Returning to the subject of the difference of the IV 

 seminal organs in various groups of male animals : blooded 

 If we are to consider the causes to which this is due, animau : 

 we must first of all understand the purpose for the parts i^ 

 sake of which " testes exist. If we agree that every- °^'* ' 

 thing which Nature does is done either because it is 

 necessary or else because it is better,'' we should expect 

 to find that this part, Uke the rest, exists for one or 

 the other of these two reasons. Now it is evident 

 that it is not necessary for generation, otherwise 

 all animals that generate would have it, whereas 

 actually neither Serpents nor Fishes have testes, and 

 these do in fact generate, because they have been 

 observed copulating, with their passages full of milt. 

 The other reason then remains : testes exist for some 

 purpose — because it is better that they should exist. 

 Now the business of most animals may be summed up 

 pretty much as that of plants is — viz., seed and fruit; 

 and,, just as (to take a parallel case) animals which 

 have straight intestines are more violent in their 

 desire for food," so here also, animals which have no 

 testes but passages only, or which have testes but not 

 external ones, are all quicker with the business of 

 copulation. Those, however, which have to be more 

 sober (a) in the case of feeding, have not straight 

 intestines, and (b) in the case of copulation, have 

 passages which are twisted,** so that their desire shall 

 not be violent or speedy. This then is the object for 

 which the testes have been contrived : they make 



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