GENERATION OF ANIMALS, III. i. 



observation that they have been formed in chickens 

 and gosUngs without impregnation. x\gain, when 

 the female partridges " which are taken out to act as 

 decoy-birds smell the male and hear his note, those 

 which have not been trodden by a male become 

 full of eggs and those which have already been 

 trodden at once lay their eggs. The reason why 

 this happens is the same as in the case of human 

 beings and quadrupeds : if they are in heat, some 

 emit the semen at the mere sight of a female, others 

 at a slight touch. Birds of this sort are by nature 

 inclined to frequent intercourse and have abundance 

 of semen, so that when they are in heat the impulse 

 they need to set them off is small, and emission 

 quickly takes place ; the result is that in those which 

 have not been impregnated -s^ind-eggs take shape, 

 and in those which have been impregnated the eggs 

 quickly grow and reach perfection. 



In the group of animals which lay their eggs exter- 

 nally, birds produce their eggs in a perfected state, 

 fish in an imperfect state ; but fishes' eggs continue 

 and finish their growth apart from the parent, as 

 indeed I have said earlier. The reason for this is that 

 the fish tribe is very prolific ; therefore it is impossible 

 for a large number of eggs to reach perfection within 

 the animal ; hence they are laid externally. Their 

 discharge is quickly effected, for in the externally 

 oviparous fishes the uterus is near the genital parts. , 



Birds' eggs are double-coloured, but all fishes' eggs Difference 

 are single-coloured. The cause of the two colours in yoi)^|*^ 

 birds' eggs can be seen from the specific character ^ white. 

 of each of the two parts, the white and the yolk. 

 The secretion (for the egg) is formed out of the blood 



* Dynamis ; see Introd. § 26. 



277 



