INCUBATION. 219 



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 anat- 

 omists ; these bulgings of the second membrane pass quite 

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

 imbedded in the white, they keep the enclosed yolk and germ 

 somewhat in a fixed position, preventing 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 

 two first, is formed around it, becoming attached to the bulg- 

 ings, 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 half-way along the oviduct. It is 

 still, however, destitute of the shell, which begins to be formed 

 by a process similar to the formation of the shell of a snail, as 

 soon as the outer layer of the third membrane has been com- 

 pleted. When the shell is fully formed, the egg continues to 

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

 lays it. 



From ill-health, or accidents, eggs are sometimes excluded 

 from the oviduct before the shell has begun to be formed, and 

 in this state they are provincially termed oon or wind eggs. 



Reckoning, then, from the shell inwards, there are six dif- 

 ferent envelopes, one of which only could be detected before 

 the descent of the egg into the oviduct. 



1. The shell. 



2. The external layer of the membrane 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 yellowish liquid on the inside. 



5. The bulgings or chalaziferous membrane. 



6. The proper membrane. 



