EVOLUTION OP THE CHICK. 



159 



The Ernbryo of the preceding 1 K^, opened to show the course of the prin- 

 ciparblood- vessels which go to the vesicle and to the areolar membrane. 



the thinness of their coats, they furnish the best object 

 for demonstrating the circulation of the blood in a 

 warm-blooded animal. According to Scarpa, the 

 thigh-bones, when dried, now preserve their shape. 



On the fourteenth day the feathers appear well 

 developed ; and if the embryo be taken out of the 

 egg, it can open its beak for the purpose of 

 breathing. 



During the remaining part of the process, the 

 yolk becomes gradually thinner and paler by the 

 intermixture of the inner white ; while an immense 

 number of fringe-like vessels, with flaky terminations 

 of a singularly peculiar structure, are formed on the 

 "aner surface of the yolk-bag, and hang into the 



