ki 
INTRODUCTIOjST. 
Trior to its exclusion, this membrane, which embraces the whole of the egg, 
indurates, and forms the shell; but it is not nearly so hard in the body of any 
bird when it has attained maturity, (except the Cuckoo) as after it has been 
exposed to the atmosphere. About the centre of the yolk lies a little 
filmy circle, containing a thin fluid, surrounding a small white speck, from 
which the bird springs : the former is called the cicatricula, and in which 
the speck floats, as in a cradle. This speck begins to expand within one 
hour after incubation, drawn into being by the external heat. It is pro- 
bable that, though it appears as a small crude, ill-formed, and ilh digested 
mass, that it contains within itself, though hidden from human sight, all 
the parts of which the bird is composed ; and which are regularly deve- 
loped by the result of the action of the vital principle, which disengages 
them from that lethargic state, in which they before reposed. Shortly 
after incubation, the cicatrice enlarges, and red blood may be discerned on 
the surface of the yolk bag, at the end of thirty- six hours. In the begin- 
ning of the third day the heart is seen to beat ; the backbone thickens, the 
head is bent ; the eyes appear, and crimson blood begins to fill the little 
vessels that lead to the heart. Its movement is then distinguished by a 
triple pulsation ; the eyes, by their immense size, and the black dense fluid 
with which they are tinged ; and the vertebrae may now be distinctly seen. 
On the fourth, the stomach, intestines, and liver appear, and a vascular 
film rises round the navel. This is supposed to supply the place of the 
respiring organs, which become discernible on the following day, but do 
not perform their office until the chick escapes from the amnios, the name 
by which the cicatricula is known when it is much enlarged. On the 
fifth, the wings unfold, and the points of the feathers appear. On the 
sixth, the chick moves voluntarily, and the abdominal viscera are greatly 
increased, and both ventricles of the heart may be discovered in active pul- 
sation. On the seventh, the juice that ossifies is secreted, and the heart 
wears the appearance of having two separate ventricles ; and two successive 
pulsations may be remarked both in the ventricles and auricles, as if there 
were two hearts. By the’eleventh day, nature has completely developed 
