Tails 403 
coverts. Mention is here made of these because of the 
‘important part they 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.316). 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 1t 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 
