26 THE STORY OF BIRD-LIFE. 



face of certain parts of the feather which 

 through the microscope are seen to be strangely 

 and wonderfully carved into fine ridges and 

 grooves, or covered with tiny dot-like papillae; 

 these act like so many prisms, and hence the 

 marvellous play of colour which so fascinates us. 

 Those who would like to know more of this 

 subject should read Dr Gadow's lucid descrip- 

 tions in the new "Dictionary of Birds," a book 

 all bird-lovers should possess. 



The beak sheath, to which we have already re- 

 ferred, constitutes the outer covering of the jaws, 

 which form what is commonly known as the 

 '•bill" or "beak" of the bird. Sometimes this 

 sheath, as in the petrels, is made up of a number 

 of pieces ; sometimes, and more generally, it 

 consists of two simple cases only, one for the 

 upper and one for the lower jaws. The various 

 forms which the beak assumes are to be dealt 

 with in our next chapter. 



The claws are the " nails " of the bird's foot 

 and vary in form, length and so on according 

 to the need of the bird. In many birds, such as 

 the heron, and night-jar, and some others the 

 claw of the middle toe bears a curious little 

 comb the purpose of which no one has yet been 

 able to discover. 



Many birds are armed with formidable spurs. 

 Sometimes these grow on the legs and sometimes 

 on the wings. The screamer, a South American 

 bird, allied to the ducks and geese, has a most 

 formidable spur on its wrist joint. The common 

 barn-door fowl bears spurs upon its legs. In the 

 olden time, when cock-fighting was a favourite 



