70 
BIRD-LIFE. 
caused by the growing together of the two flakes, or 
laminae, of the skin of the germ goes on further; the 
upper laminae close themselves completely on the fifth 
day into that envelope, to which I gave the name of 
cradle. The vertebrae become lengthened in such a 
manner that the head and tail portions almost touch, 
through the curved position they occupy; the eyes 
exceed in development almost all the remaining parts. 
The processes of the legs and wings, which on the third 
day of incubation were only visible as slight ridges, and 
on the fourth as projecting leaves to the plate of the 
stomach, became on the fifth day rather prominent 
stumps. At the close of the last-named day what still 
remains of the egg has become essentially changed in 
appearance: the albumen, or white, has considerably 
decreased, and the yolk, on the contrary, increased; the 
latter has acquired more substance, while the former has 
become more fluid in its consistency. 
Now commences quite a new stage of the exist¬ 
ence of our creature. With the sixth day appears a 
hitherto dispensable, but now highly important organ, 
which in the meantime does the duty of the lungs, the 
allantois. This appears already, the second day the egg 
has become vivified, in the form of a small globule situate 
at the hinder part of the germinating chick: this 
increases on the third day but slowly; from the sixth, 
however, its progress is very rapid. Whereas, in the 
meantime, the breast and belly have closed up, except 
where the umbilical opening is connected by a tube with 
the yolk, there remains no other means of communication 
open for it: consequently it is connected with the body 
by one of the tubes which pass through the navel, and is 
not brought into closer contact with the yolk or nutrition 
