B. VI.] THE HISTORY OF AXIMALS. 1.41 



but if the act is repeated, a rapid increase in size takes place. 

 The nature of the white and yolk of the egg is different, not 

 only in colour, but in other properties, for the yolk coagu- 

 lates with cold, while the white remains fluid, but the white 

 coagulates with heat, which the yolk does not, but remains 

 soft, if it is not burnt ; and it becomes consistent and dry 

 by boiling rather than roasting. 



8. The white and yolk are separated from each other by 

 a membrane. The chalaza3 at the extremities of the yolk 

 have nothing to do with generation, as some persons suppose. 

 These spots are two, one below and one above. If many 

 whites and yolks of eggs are taken out, and mixed together 

 in a vessel, and cooked with a slow and moderate heat, 

 the yolks will all collect in the middle, and the whites will 

 surround them. Young domestic fowls begin to lay eggs at 

 the beginning of the spring; they lay more than those 

 which are older, but those of the young birds are smaller, 

 and if birds are not permitted to incubate, they are de- 

 stroyed and become sick. 



9. After copulation birds ruffle and shake themselves, 

 and often cover themselves with chaff, and this also they do 

 when they have laid. Pigeons draw up their tail, geese 

 go and bathe. The pregnancy and conception of barren 

 eggs is quick in most birds, as in the partridge, on ac- 

 count of the violence of their sexual desires ; for if the hen 

 stands in the way of the breath of the male, she con- 

 ceives, and ^immediately becomes of no use for fowling ; for 

 the partridge appears to have a very distinct smell. The 

 production of the egg after copulation, and the production 

 of the young by incubation, do not occupy the same length 

 of time in all birds, but varies according to their size. The 

 egg of the domestic fowl is perfected in ten days after 

 sexual intercourse, and that of the pigeon in a shorter time. 

 Pigeons are able to retain their eggs even in the act of 

 parturition. If they are disturbed by anything occurring 

 in the neighbourhood of their nest, or a feather be plucked 

 out, or if anything else troubles or disturbs them, they re- 



'tain the egg they were about to lay. 



10. This is peculiar to pigeons, and so is the following : 

 for they kiss each other when the male is about to mount, 

 or else they will not endure it. The older bird lirst gives 



