Chap. VII.] THEORY OF NATURAL SELECTION. 289 



serving for the widely different purpose of securing live 

 fish. 



Beturning to the whales. The Hyperoodon bidens 

 is destitute of true teeth in an efficient condition, but 

 its palate is roughened, according to Lacepede, with 

 small, unequal, hard points of horn. There is, therefore, 

 nothing improbable in supposing that some early Ceta- 

 cean form was provided with similar points of horn on 

 the palate, but rather more regularly placed, and which, 

 like the knobs on the beak of the goose, aided it in seizing 

 or tearing its food. If so, it will hardly be denied that 

 the points might have been converted through variation 

 and natural selection into lamellae as well-developed as 

 those of the Egyptian goose, in which case they would 

 have been used both for seizing objects and for sifting 

 the water ; then into lamellae like those of the domestic 

 duck ; and so onwards, until they became as well con- 

 structed as those of the shoveller, in which case they 

 would have served exclusively as a sifting apparatus. 

 From this stage, in which the lamellae would be two- 

 thirds of the length of the plates of baleen in the Balae- 

 noptera rostrata, gradations, which may be observed 

 in still-existing Cetaceans, lead us onwards to the enor- 

 mous plates of baleen in the Greenland whale. Nor is 

 there the least reason to doubt that each step in this 

 scale might have been as serviceable to certain ancient 

 Cetaceans, with the functions of the parts slowly changing 

 during the progress of development, as are the gradations 

 in the beaks of the different existing members of the 

 duck-family. We should bear in mind that each species 

 of duck is subjected to a severe struggle for existence, 

 and that the structure of every part of its frame must 

 be well adapted to its conditions of life. 



