Forma tiox of the Egg. » 



37 



eggs are of different sizes, according to the different degree of development, and during 

 the period of laying are constantly coming to maturity in due succession, so as to keep up the 

 supply of eggs with which we are so familiar. It is worthy of remark that from the germ of 

 every egg a narrow passage or canal runs to a small chamber in the centre of the yolk, which 

 can be readily seen if the yolk of a hard-boiled egg be cut across. 



As the yolk becomes fully matured, the enclosing membrane or ovisac becomes thinner 

 and thinner, especially round its greatest diameter or equator, which then exhibits a pale zone 

 or belt called the stigma. Finally fecundation takes place, the sac ruptures at the stigma, 

 and the liberated yolk and germ, surrounded by a very thin and delicate membrane, is received 

 by the funnel-shaped opening of the oviduct or egg-passage, whose 

 office it is to convey it to the outer world, and on its way to clothe 

 it with the other structures needful for its development and preser- 

 vation. This organ, with its various convolutions a little modified 

 for convenience of representation, is shown at Fig. 17, and in an 

 ordinary hen is nearly two feet in length. It will easily be seen 

 that not unfrequently two yolks may become detached and enter 

 the oviduct at nearly the same time ; in which case they are very 

 likely to be enveloped in the same white and shell, causing the 

 " double egg " so well known to every poultry-keeper. 



Thus received into the oviduct, the yolk becomes enveloped 

 in a glairy fluid called the white, or by chemists albumen. This 

 is secreted by the mucous membrane of the oviduct, and added 

 layer by layer as the &gg passes on. These different layers can 

 be easily seen, and even peeled off in succession when an egg is 

 hard-boiled. The uses of the white or albumen are manifold. It 

 is eminently nutritious, forming, indeed, the chief nourishment of the 

 chick during its growth in the shell ; as it becomes absorbed by 

 the little animal, and forming as it does by far the greater part 

 of the egg when laid, it gives the fast-growing little body the needed 

 increase of room ; it is a very bad conductor of heat, and hence 



guards the hatching egg against the fatal chills which would otherwise occur when the hen left 

 the nest ; and finally, it preserves the still more delicate yolk and vital germ from concussion 

 or other violent injury. The manner in which the last purpose is effected is very beautiful. 

 Besides the ordinary white, two longitudinal cords or strings of much denser and even slightly 

 fibrous albumen are formed, which are easily distinguished if an egg be broken into a basin. 

 These cords are termed the chalazce, and are attached in a spiral form to the under side of 

 the yolk, to which they therefore serve as ballast or weights, and always keep the germ uppermost, 

 where it can best receive the heat from the sitting hen. 



At a still further point of the oviduct the egg becomes invested with the skin or parchment- 

 like covering which is found inside the shell, and is called by physiologists the membrana 

 'p7itaminis. In reality this skin consists of two layers, which can easily be separated ; and in fact 

 at the large end of the egg they do separate entirely, forming what is commonly called the 

 air-bubble, or by anatomists the vesicula ceris. How formed is still a mystery ; but it is an 

 ascertained fact that the air in this bubble or chamber contains a far larger portion of oxygen 

 than the atmosphere. At first the chamber does not exceed a quarter of an inch in diameter, 

 but as the egg gets stale it becomes larger and larger, so that even in eggs stored it fills 



'ig- 17- 



