GENERATION OF ANIMALS, I. xviii.-xix. 



produce residue both from the fluid nourishment and 

 from the soHd, the semen is discharged by the same 

 exit as the fluid residue, because it is itself a residue 

 from a fluid, the nourishment of all animals tending 

 to be fluid rather than solid ; (6) in those animals 

 which produce no fluid residue, the semen leaves by 

 the same way as the solid excrement. Further, 

 colUquescence is always morbid, whereas the removal 

 of residue is beneficial ; and the discharge of semen 

 has both characteristics because it includes some of 

 the useless nourishment. If it were just a colliques- 

 cence, it would always be injurious, whereas in fact 

 it is not so.] 



To conclude : the foregoing discussion makes it 

 clear that, whether all animals discharge semen or 

 not, semen is a residue derived from useful nourish- 

 ment, and not only that, but from useful nourishment 

 in its final form. 



Our next task is to detemiine what is the character XIX 

 of the nourishment from which this residue is derived ; Menstrual 

 and we must discuss the menstrual discharge as well, 

 because this occurs in some of the Vi\dpara. By this 

 means we shall be able to give a clear answer to 

 the following questions : Does the female discharge 

 semen as the male does, which would mean that the 

 object formed is a single mixture produced from 

 two semens ; or is there no discharge of semen from 

 the female ? And if there is none, then does the 

 female contribute nothing whatever to generation, 

 merely providing a place where generation may 

 happen ; or does it contribute something else, and if 

 so, how and in what manner does it do so ? 



We have said before ** that in blooded animals 

 blood is the final form of the nourishment, and in 



89 



