Tails 



403 



coverts. Mention is here made of these because of the 

 important part the}' take in certain sham tails which 

 will soon be described. 



In the embryos of most birds of true flight the tail- 

 tip of the back-bone is represented by six or ten separate 

 pieces, which, before the chick hatches from the egg, 

 fuse into the ploughshare bone. In the ostrich-like birds 



Fig. 317. — Tail-bones of Bald Eagle, showing greater fusion and more 

 specialization than in Fig. 316. 



these small bones never fuse, but remain separate through- 

 out life — a reptilian character persistent in these strange 

 birds (Fig. 3 16). The ploughshare bone is seen splendidly 

 developed in such a bird of strong flight as the Bald Eagle. 

 Now that we have explained the origin of the tail, 

 let us consider what part it plays in the lives of the birds 

 about us. So diverse are the modes of life, and so varied 

 are the surroundings of this class of creatures, that we 



