THE BIRDS 265 



iridescence caused by the light falling on the surface of the feather, 

 which may be ridged, polished or pitted, and beneath which lies 

 a blackish pigment, so that the surface acts as a series of prisms. 

 But, alas, 1 " this fatal gift of beauty has from earliest times subjected 

 the wearers to a rigorous persecution, not only at the hands of 

 savage races, but of peoples boasting themselves civilised, among 

 whom women have always been the worst and most heartless 

 offenders. On account of the ceaseless persecution to which these 

 defenceless creatures have been subjected to meet the demands 

 of fashion, savage and ' civilised/ many species have become wiped 

 out of existence, and of many more the doom is sealed ; the more 

 beautiful of the humming-birds and the birds of paradise, for 

 example, will, in another decade, have ceased to exist ! " 



At the base of the tail feathers birds have, as a rule, an oil- 

 gland, or uropygium, in which is secreted a considerable quantity 

 of clear oil. This oil is generally believed to be used by birds to 

 lubricate their plumage ; they are said to press out a small quantity 

 with their beaks, through which they afterwards draw the feathers 

 separately, This fact has, however, lately been disputed by several 

 ornithologists, as the beaks of many birds are so constructed that 

 it is impossible for them to perform the operation, and it has been 

 suggested that possibly the gland may act as a scent gland. 



Existing birds are divided into two separate orders : the first, 

 the Carinatce, includes all the flying birds ; and the second, the 

 Ratita, the running birds ostriches, cassowaries, etc. A third 

 order, the Saururcz, comprises the extinct, lizard-tailed birds. 



The breast-bone, or sternum, of a bird is large and broad, and 

 more or less convex in shape. In all flying birds it is provided 

 with a ridge or keel (carina), to which is attached the powerful 

 flight muscles by which the wings are moved. The keel varies in 

 size according to the power of flight of the particular species 

 thus, swifts, certain petrels, and humming-birds have a remarkably 

 deep keel on the breast-bone, while in some of the rails and certain 

 extinct birds, such as the New Zealand goose and the dodo, the 

 keel is hardly discernible. The running birds ostriches, emus, 

 etc. have no keel to the sternum, and are termed raft-breasted 

 birds (Ratitce}. 



A bird's skull is remarkable for the large size of the eye sockets, 



1 W. P. Pycraft. 



