GENERATION OF ANIMALS, III. i. 



lay often, producing two, or three at the most, gener- 

 ally two, as these numbers are intermediate between 

 one and many. 



The actual facts make it clear that in the prolific 

 birds the nourishment is diverted to the semen. Most 

 trees, if they have borne an excessive amount of 

 fruit, A^-ither away when the 'crop is over, when no 

 nourishment is left over for themselves ; annual 

 plants, as it seems, have the same experience, e.g., 

 leguminous plants, corn, and the rest of that sort. 

 The reason is that, as they belong to a kind which 

 produces a great deal of seed, they use up all their 

 nourishment for semen (seed). Some fowls, too, 

 after having laid excessively — as many as two eggs 

 in a day — have died after performing the feat. The 

 birds and plants alike become completely exhausted, 

 and this condition is simply one of excessive evacua- 

 tion of residue. It is responsible for the sterility 

 which besets the lion in the latter part of its life. 

 To begin with, the lion " will produce five or six cubs 

 in a Utter, then four the next year, next time three, 

 then two, after that one, and then none at all, which 

 suggests that the residue is being used up and that 

 the semen is diminishing as the prime of life abates. 



We have now said which are the birds that produce 

 wind-eggs, and what sorts of birds are prolific and not 

 prolific, together with the causes thereof. 



Why are wind-eggs formed ? As has been said Wind-eggs. 

 earlier, their formation is due to the fact that though 

 seminal matter is present in the female, with birds no 

 discharge of the menstrual fluid take place as it does 

 with the blooded Vivipara ; in all of the last-named 

 it does take place, and it is greater in some, smaller 



" Cf. 760 b 23. 



271 



