GENERATION OF ANIMALS, I. xxi. 



that there is no necessity for any substance to pass 

 from the male ; and if any does pass, this does not 

 mean tfiat the offspring is formed from it as from 

 something situated \\-ithin itself during the process, 

 but as from that which has imparted movement to it. 

 or that which is its " form." The relationship is the 

 same as that of the patient who has been healed 

 to the medical art. (6) This piece of reasoning is 

 entirely borne out by the facts. It explains why 

 certain of those males which copulate with the 

 females are observed to introduce no part at all into 

 the female, but on the contrary the female intro- 

 duces a part into the male. This occurs in certain 

 insects.** In those cases where the male introduces 

 some part, it is the semen which produces the effect 

 inside the female ; but in the case of these insects, 

 the same effect is produced by the heat and dynamis 

 inside the (male) animal itself when the female in- 

 serts the part which receives the residue. And that 

 is why animals of this sort take a long time over copu- 

 lation, and once they have separated the young 

 are soon produced : the copulation lasts until (the 

 dynamis in the male) has " set " (the material in the 

 female), just as the semen does ; but once they 

 have separated they soon discharge the fetation, ** 

 because the offspring they produce is imperfect ; all 

 such creatures, in fact, produce larvae. 



However, it is the beha\'iour of birds and the group 

 of o\iparous fishes which pro\ides us ^^^th our 

 strongest proof (a) that the semen is not drawn from 

 all the parts of the body, and (6) that the male does 

 not emit anv part such as will remain situated within 

 the fetus, but begets the young animal simply by 

 means of the dynamis residing in the semen (just as 



115 



