GENERATION OF ANIMALS, I. xxi.-xxii. 



tion the contribution which the female makes to the 

 embryos when they are being " set " and constituted 

 is on different lines from that of the male ; in other 

 words, the male contributes the principle of move- 

 ment " and the female contributes the material. This 

 is why (a) on the one hand the female does not gener- 

 ate on its own : it needs some source or principle to 

 supply the material >rith movement and to determine 

 its character (though in some (female) animals, as in 

 birds, Nature can generate up to a point : the females 

 of these species do actually " set " a fetation, but 

 what they " set " is imperfect, xiz., what are kno^^^l 

 as wind-eggs) ; (6) on the other hand, the formation XXII 

 of the young does in fact take place in the female, 

 whereas neither the male himself nor the female 

 emits semen into the male, but they both deposit 

 together what they have to contribute in the female 

 — it is because that is where the material is out of 

 which the creature that is being fashioned is made. 

 And as regards this material, a good quantity of it 

 must of necessity be available immediately, out of 

 which the fetation is " set " and constituted in the 

 first place, and after that fresh suppUes of it must 

 be continually arri\'ing to make its growth possible. 

 Hence, of necessity, it is in the female that parturi- 

 tion takes place. After all, the carpenter is close by 

 his timber, and the potter close by his clay ; and to 

 put it in general terms, the working or treatment of 

 any material, and the ultimate movement ° which 

 acts upon it, is in all cases close by the material, e.g., 

 the location of the activity of house-building is in the 

 houses which are being built. These instances may 

 help us to understand how the male makes its con- 

 tribution to generation ; for not every male emits 



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