ADAPTATIONS 425 



stages in the development of the Owls (see p. 439), which 

 live now on the flesh of the higher vertebrates. The step from 

 an insectivorous diet to a diet of the flesh of vertebrates is but 

 a short one, and vice versa. Indeed many confirmed " flesh- 

 eaters " live occasionally on insects. For example, I have 

 commonly found the stomach of the Short-eared Owl {Asio 

 brachyotus) crammed with the Common Dor-beetle {Geotrupes 

 vernalis). 



While the modifications hitherto described are all of a kind 

 that are characteristic of a large number of species, and differ 

 only in degree one from another, there are a few which are 

 unique, that is to say, they are met with only in a single species, 

 or at most in three or four. In some of these the correlation 

 between the method of feeding and the shape of the beak is 

 evident, in others no such insight is possible. 



The little Wry-billed Plover of New Zealand is an instance 

 where this correlation can be plainly seen. In this bird (Ajia- 

 rhyncJius frontalis) the beak is drawn out to a fine point and 

 curves sharply to the right, a formation which enables the bird 

 to pick up small Crustacea lurking under stones between tide- 

 marks. So nice is the adjustment between this structural 

 modification and the habit of feeding that the bird invariably, 

 when hunting, walks round the stone left to right ! Further, the 

 black band which encircles the breast is broadest on its left, or 

 exposed side, and this because the band is a device adopted for 

 protective purposes, enabling the bird more closely to resemble 

 its surroundings ! No less remarkable is the beak of the Scissor- 

 bill {R/iyndops nigra). This bird is hardly to be separated 

 from the Terns {Sterna), yet the beak is absolutely unlike that 

 of any other known bird, the lower jaw being much longer 

 than the upper (111. 47, p. 413), and both being flattened to the 

 thinness of a knife-blade from the gape forwards ! In feeding, 

 the Scissor-bill skims along the surface of the water with the 

 lower blade thrust into the stream. By this plan toll is taken 

 of shoals of small fishes swimming at the top of the water, the 

 fish being caught up as by a pair of shears as the bird passes 

 over them. In the nestling (111. 47, p. 413), it is to be remarked, 

 the jaws are of equal length. 



A species of Stork known as the "Open-bill" {Anastomus) 

 p. 362 has the upper and lower jaws curiously bowed so as to 



