Development of the Chick „ 
39 
the eyes are clearly distinguishable, the leathers have begun to be formed, scales are perceptible 
on the legs, and the skeleton has assumed an evident bony consistence. About this time also 
movement is perceptible, and the allantois , or respiratory membrane, exhibits a very complex 
and beautiful series of blood-vessels, which draw air rapidly through the shell, and act as lungs to 
Fig. 1 8. 
Fig. 19. 
Fig. 20. 
the now fast-growing chicken. The development of the chick at the eleventh day is shown 
in Fig. 19. From this date the various organs mature steadily and rapidly: till about the nine- 
teenth day' the beak of the chick ruptures the air-bubble at the end of the egg, now become 
very much enlarged, and the chick for the first time breathes through the lungs. The immediate 
result of thus inhaling the air is a stimulation which produces very lively motion, so that the egg 
if now placed in warm water moves about in a most curious manner, as already stated. The 
development, as seen in Fig. 20, is now very perfect ; indeed, little difference can be observed 
between the present stage and the perfect chick, except that the yolk, shown in the figure, and 
more clearly represented in Fig. 21, is not yet drawn into the abdomen, where, as before observed, 
Fig. 21. — Chick two days before exclusion. 
it is destined for the food of the newly-hatched bird. This is however rapidly accomplished, 
when the chick is ready for entrance into the outside world. 
The chick breaks the shell by giving two or three smart taps every now and then with a sharp- 
