ADAPTATIONS 419 



strainer. In the Swans these structures are carried a step 

 further : but they attain their highest perfection in the Ducks, 

 reaching the maximum development in the Shoveller where 

 these lamellse are relatively of enormous length, recalling 

 the baleen plates of certain whales. Some of the Ducks have 

 further modified the structure of the beak. Thus the Blue 

 Duck of New Zealand [Hyptenolcemus) has developed mem- 

 branous folds on each side of the upper jaw, and these prob- 

 ably have some relation to the capture of insect larvae on 

 which this bird is said to live. The Mergansers have long, 

 narrow beaks, the edges of which are armed with sharp, back- 

 wardly directed tooth-like processes adapted for the capture 

 offish (111. 47, p. 41 3). In these birds the tongue differs conspicu- 

 ously from that of other Ducks, being less fleshy, and only 

 feebly provided with the lateral processes so characteristic of 

 the Ducks. 



While the serrations of the beak in the Diving-ducks and 

 Geese bear a rough semblance to horny conical teeth, in some 

 birds these serrations take the form either of a series of fine 

 needle-like points, as in the Darters {Plotus), for example, or 

 of a number of extremely minute and sharp-pointed notches, 

 as in the Sun-birds. But between these two extremes many 

 intermediate types are to be met with. 



Where the food has to be torn or finely divided we find 

 the beak short, hooked and pointed, as in the Carrion-feeding 

 Vultures, the Hawks, Eagles, Owls, and the Shrikes, and it 

 presents a similar shape in the rodent Parrots which feed upon 

 fruits and other vegetable matter. Thus it will be seen that the 

 superficial resemblance which beaks may present is a danger- 

 ous guide as to questions of affinity. 



The beaks of Parrots illustrate in an even more striking 

 manner than in the case of the Finches (p. 405) how close may 

 be the relation between the form of the jaws and the nature of 

 the food. 



In these birds the whole structure of the skull has been 

 transformed to facilitate the manipulation of food. In the 

 first place the upper jaw articulates with the frontal bones by 

 means of a hinge, while the palatine bones have been enorm- 

 ously developed so as to form deep blades of bone set on edge 

 and terminating at the base of the premaxilla. The details 



