THE DOMESTIC FOWL. 101 



oviduct. It is proper to mention, also, that this second 

 membrane, enveloping the yolk and the germ of the 



• chick, is thickest at the two ends, having what may- 

 be called bulgings, termed chalazes by anatomists ; 

 these bulgings of the second membrane pass quite 

 through the white at the ends, and being thus as it 

 were embedded in the white, they keep the inclosed 

 yolk and germ somewhat in a fixed position, prevent- 

 ing them from rolling about within the egg when it is 

 moved. The white of the egg being thus formed, a 

 third membrane, or rather a double membrane, much 

 stronger than either of the first two, is formed around 

 it, becoming attached to the bulgings, or chalazes, of 

 the second membrane, and tending still more to keep 

 all the parts in their relative positions. " 



During the progress of these several formations, the 

 egg gradually advances about halfway along the ovi- 

 duct. It is still, however, destitute of the shell, which 

 begins to be formed by a process similar to the forma- 

 tion of the shell of a snail, as soon as the outer layer 

 of the third membrane has been completed. When 

 the shell is fully formed, the egg continues to advance 



•along the oviduct, till the hen goes to her nest and 

 lays it. 



Reckoning, then, from the shell inwards, there are 

 six different envelopes, one of which only could be de- 

 tected before the descent of the egg into the oviduct :— 

 1. The shell. 2. The external layer of the mem- 

 brane lining the shell. 3. The internal layer of the 

 same lining. 4. The white, composed of a thinner 

 liquid on the outside, and a thicker and more yellow- 

 ish liquid on the inside. 5. The bulgings, or chala- 

 ziferous membrane. 6. The proper membrane. 



One important part of the egg is the air bag, or 



folliculus aeris, of anatomists, placed at the larger 

 end, between the shell and its lining membranes. Ac- 

 cording to Dr. Paris, it is about the size of the eye of 

 a small bird in new-laid eggs, but is increased as much 

 as ten times in the process -of hatching. 



