GENERATION OF ANIMALS, I. xiii.-xv. 



the very outset [at the same time as the passages] ; 

 and similarly in those animals whose testes are ex- 

 ternal. Afterwards they meet and unite towards 

 the region of the pudendum. The arrangement of 

 the passages is the same as this in dolphins, although 

 their testes are hidden below the abdominal cavity. 



We have now described the situation of the parts 

 which are concerned with generation in the blooded 

 animals and have stated the causes. 



In the other class of animals, viz., the bloodless XIV 

 ones, the manner of the parts concerned with genera- bloodless 

 tion is quite different from what it is in the blooded animals. 

 ones ; and what is more they differ among them- 

 selves. We have here four groups still left to deal 

 with : (1) Crustacea, (2) Cephalopods, (3) Insects, 

 (4) Testacea (with regard to all of these the facts 

 are obscure, but it is plain that most of them do 

 not copulate " ; as for the manner in which they 

 arise, we must describe this later on).^ (1) The (i) Crus- 

 Crustacea copulate as the retromingent animals do : 

 one lies prone and the other supine and they fit their 

 tail-parts one tp the other. The males are prevented 

 from mounting the females belly to back by their 

 tail-parts which have long flaps attached to them. 

 The males have narrow seminal passages, and the 

 females have a membranous uterus by the side of the 

 gut, divided on either side, and in this the egg is 

 formed. (2) The Cephalopods copulate by the XV • 

 mouth, pushing against each other and intertwining (2) Cepha- 

 their tentacles. This manner of copulation is due to 

 necessity, because nature has bent the end of the 

 residual passage so as to bring it round by the side of 

 the mouth, as I have previously said [in the treatise 



* Book III, ell. 11. 



43 



