GENERATION OF ANIMALS, IV. vni.-x. 



events, no menstrual evacuations take place during 

 the suckHng period, nor do women conceive then ; 

 and if they do conceive, the milk dries up, because 

 the nature of the milk is the same as that of the men- 

 strual fluid, and Nature cannot produce a plentiful 

 enough supply to provide both ; so that if the secre- 

 tion takes place in one direction it must fail in the 

 other, unless some violence is done contrary to what 

 is normal. And that ipso facto means something 

 contrary to Nature, because in the. case of things 

 which admit and do not exclude the possibility of 

 being other than thev are, " normal " and " natural " 

 are identical. 



In the actual birth of the young animals we have 

 another instance of good timing. When the nourish- 

 ment that passes through the umbilical cord is no 

 longer sufficient for the fetus, owing to its size, at 

 that same time the milk is becoming serviceable, and 

 when no nourishment is entering by way of the 

 umbilical cord, then the blood-vessels to which the 

 cord acts as a sheath collapse ; and for these reasons 

 and at that time the exit of the fetus takes place. 



The natural manner of birth for all animals is head IX 

 first, because they have a larger bulk above the ^^OTn"head 

 umbilical cord than below it, so that they are sus- foremosc. 

 pended from it, as it might be in a balance, and the 

 heavier side {i.e., the larger parts) goes down. 



The period of gestation is of a definite length for X 

 each of the animals, and normally the periods are ^p^Jift^onf 

 proportionate to the animals' span of life ; after all, period. 

 we should expect those which have a longer life- 

 span to take longer over their formation than others. 



'" hie in Z spatium xi vel xii litterarum. 

 * Xpovuorepwv P : ■xpovuav vulg. 



475 



