GENERATION OF ANIMALS, III. i. 



duce an egg of one colour only, but this egg is imper- 

 fect — its growth takes place away from the parent, 

 and the Cause concerned '^ is just the same as for ' 

 those eggs which are perfected -v^ithin the parent. 



I have already spoken about the uterus of these 

 animals ; I have said what are the differences they 

 show, and what are the Causes. Thus, some of the 

 %-iviparous animals (the Selachian fishes) have the 

 uterus high up towards the diaphragm.^ others 

 (the animals which are both internally and externally 

 vi\iparous, such as man, horse, and all such animals) 

 have it down by the pudenda. And of the oWparous 

 animals some (such as the oviparous fishes) have it 

 low down, others (such as the birds) have it high up. 



Fetations arise in birds spontaneously as well (as (i.) Birds 

 in the normal way) ; some people call them ^\"ind- 

 eggs or zephyria.'^ They occur in those birds ^ which 

 are neither good fliers nor crook-taloned but which 

 are prohfic* The reason is : (a) these have a great 

 deal of residue, whereas in the crook-taloned birds 

 this secretion is diverted to produce wings and vnng 

 feathers and their body is small f and solid and hot ; 

 and (6) the menstrual secretion and the male semen 

 are residue ; therefore, as both feathers and semen 

 alike are formed out of residue. Nature cannot pro\ide 

 a large supply for both purposes. And it is for this 

 same cause that the crook-taloned birds do not 

 indulge much in copulation and are not very prohfic, 



* See note on 717 a 2. 



■= See note on 753 a 2-2. 



' See table of birds, p. 368. 



* i.e., produce a large number of eggs (or j'oung). I use 

 " prolific " throughout to translate noXvyovos and ttoXvtokos. 



' For the smallness of the body of crook-taloned birds 

 (apart from their wings), cf. P. A. 694 a 8 f . 



265 



