GENERATION OF ANIMALS, III. i. 



coloured — they are white, judged by the colour of 

 ordinary yolk ; yellow, judged by ordinary white. 

 Not only the eggs but also the wind-eggs of birds 

 have this double colouring, because they contain that 

 out of which each of the two parts is to come (the part 

 from which the " principle " arises and that from 

 which the nourishment is derived), although they are 

 imperfect, i.e., they lack the male factor ; since, as 

 we know, wind-eggs become fertile if they are im- 

 pregnated by the male ^^^thin a certain time. The 

 cause of the double colouring is not the two different 

 sexes (as if the white were derived from the male and 

 the yolk from the female) ; both alike are derived 

 from the female, and the real difference is that one is 

 cold and the other hot. So then, in cases where a 

 good deal of the hot constituent is present, the hot 

 substance is separated from the cold ; but if there is 

 not much of it this cannot occur ; and that is why the 

 fetations of such animals are single-coloured, as I 

 have said. All that the semen does is to " set " the 

 fetations, and that is why in birds the fetation is small 

 and white in appearance at first, but completely 

 yellow as it advances and more bloodlike matter is 

 continually being mixed in with it ; finally, as the hot 

 substance separates off, the white takes up its posi- 

 tion around on the outside " evenly in every direction, 

 just as when a liquid boils. <I make this compari- 

 son), because the white (a) is in its nature liquid, and 

 (6) contains in itself the soul-heat. Therefore it 

 separates off (and arranges itself) all round (on the 

 outside), while the yellow earthy part separates off 

 within. Also, if anyone pours a number of eggs 

 together into a bladder or some such receptacle and 

 then boils them up by means of a fire which does not 



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