218 THE POULTRY-BOOK. 



CHAPTER XIII. 



INCUBATION. 



BEFORE describing the interesting process of incubation, it 

 is desirable to give some account of the structure of the egg. 

 In a laying hen may be fOund, by opening the body, what is 

 called the ovarium, which is a cluster of rudimental eggs, of 

 different sizes, from very minute points up to shapes of easily 

 distinguished forms. These rudimental eggs have as yet no 

 shell or white, which are exhibited in a different stage of 

 development, but consist wholly of yolk, on the surface of 

 which the germ of the future chicken lies. The yolk and the 

 germ are enveloped by a very thin membrane. 



" When the rudimental egg, still attached to the ovarium, 

 becomes larger and larger, and arrives at a certain size, either 

 its own weight, or some other efficient cause, detaches it from 

 the cluster, and makes it fall into a sort of funnel, leading to a 

 pipe, which anatomists term the oviduct. 



Here the yolk of the rudimental egg, hitherto imperfectly 

 formed, puts on its mature appearance of a thick yellow fluid, 

 while the rudimental chick or embryo, lying on the surface at 

 the point opposite to that by which it had been attached to the 

 ovarium, is white, and somewhat paste-like. 



The white, or albumen, of the egg now becomes diffused 

 around the yolk, being secreted from the blood-vessels of. the 

 egg-pipe, or oviduct, in the form of a thin, glairy fluid ; and 

 it is prevented from mixing with the yolk and the embryo 

 chick by the thin membrane which surrounded them before 

 they were detached from the egg-cluster, while it is strength- 

 ened by a second and stronger membrane, formed around the 

 first, immediately after falling into the oviduct. It is proper 



