200 THE FOUNDATIONS OF ZOOLOGY 



with hard, round knobs. The edges of the lower mandible are 

 serrated with teeth much more prominent, coarser, and sharper 

 than' in the duck. The common goose does not sift the water, 

 but uses its beak exclusively for tearing or cutting herbage, 

 for which purpose it is so well fitted that it can crop grass 

 closer than almost any other animal. There are other species of 

 geese in which the laminae are less developed than in the common 

 goose. 



" We thus see that in a member of the duck family with a beak 

 constructed like that of the common goose, and adapted solely for 

 grazing, or even a member with a beak having less well developed 

 laminae, might be converted by small changes into a species like 

 the Egyptian goose, — this into one like the common duck, — and, 

 lastly, into one like the shoveller, provided with a beak almost 

 exclusively adapted for sifting the water ; for this bird could hardly 

 use any part of its beak except the hooked tip for seizing or tearing 

 solid food. 



" Returning to the whales. The Hypcroddon bideiis is desti- 

 tute of true teeth in an efificient condition, but its palate is 

 roughened with small, unequal points of horn. There is, there- 

 fore, nothing improbable in supposing that some early Cetacean 

 form was provided with similar plates of horn on the palate, but 

 rather more irregularly 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 con- 

 verted through variation and natural selection into laminae as well 

 developed as those of the Egyptian goose, in which case they 

 would have served exclusively as a sifting apparatus. From this 

 stage, in which the laminae would have been two-thirds of the 

 plates of baleen of the Balcenoptera rostrata, gradations, which 

 may still be observed in existing Cetaceans, lead us onwards to 

 the enormous 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 existing 

 members of the duck family. We should bear in mind that each 

 species of duck is subjected to a severe struggle for existence, 



