34,2 Sir Everard Home on the changes the egg undergoes 
whether it is impregnated or not. Plate XXXII. fig. 10, 
11 , 12 . 
When the shell and membranes under it are removed from 
one side, the yelk appears to be kept in its place by the poles, 
although allowed to rotate upon its axis. 
The gelatinous molecule, with its areola, is always found 
upon the highest point of the upper surface of the yelk. Whe- 
ther this arises from the molecule, or from the areola being 
the lightest part of the yelk, has not been ascertained. 
When the hen begins to sit, a new laid egg, which has not 
been allowed to cool, will have the rudiments of the embryo 
formed some hours sooner than in the other eggs. 
Having traced the formation of the egg itself through all 
the changes that take place from the time the yelk leaves 
the ovarium till it is impregnated, we are now to follow those 
changes that are met with during incubation till the em- 
bryo becomes a completely formed chicken. 
In ^ hours after incubation the outer edge of the areola had 
become enlarged, and that part of it next the molecule ap- 
peared darker. One end of the molecule appeared like a 
white line, the first rudiments of the embryo. Plate XXXIII. 
fig. i, 2, 3. 
In 8 hours , the white line was found to be extended, and 
the rudiments of a brain and spinal marrow were formed, 
surrounded by a membrane, which afterwards becomes 
amnion. 
The areola had extended itself, and the surface beyond the 
line which formed its boundary had acquired the consistence 
of a membrane, and had also a distinct line by which it was 
