EVOLUTION OF THE CHICK. 157 



The Embryo Chick taken from the preceding Egg, with the amnion and 

 vesicle removed. 



was now that Scarpa first observed the wrinkles in 

 the leg and thigh-bones to become rough and hard, 

 and red spots to appear. 



On the twelfth or thirteenth day, if the membrane 

 (chorion) enveloping the white of the egg be ex- 

 amined by very cautiously opening the shell, it will 

 present, Blumenbach says, without any artificial in- 

 jection, one of the most splendid spectacles that 

 occurs in the whole organic creation, the most 

 simple, yet the most perfect substitute for the lungs. 

 It exhibits a surface covered with countless blood- 

 vessels, venous and arterial, branching through its 

 texture. The veins are of a bright scarlet colour, 

 carrying oxygenated blood to the chick ; while the 

 arteries, on the other hand, are of a deep crimson or 

 livid red, bringing the carbonated blood from the 

 body of the embryo. The functions of the two are 

 thus the reverse of those they perform after the chick 

 respires. From the trunks of these arteries being 

 connected with the iliac vessels, and on account of 



