THEORY OF NATURAL SELECTION. 319 



ting 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, as I hear from Mr. Bartlett, in 

 which the lamellae are less developed than in the common 

 goose. 



We thus see that a member of the duck family, with a 

 beak constructed like that of a common goose and adapted 

 solely for grazing, or even a member with a beak having 

 less well-developed lamellae, 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 tear- 

 ing solid food. The beak of a goose, as I may add, might 

 also be converted by small changes into one provided with 

 prominent, recurved teeth, like those of the Merganser (a 

 member of the same family), serving for the widely differ- 

 ent purpose of securing live fish. 



Eeturning 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, noth- 

 ing improbable in supposing that some early Cetacean 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 tear- 

 ing its food. If so, it will hardly be denied that the points 

 might have been converted through variation and natural 

 selection into lamellse 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 on- 

 ward, until they became as well constructed as those of the 

 shoveller, in which case they would have served exclusively 

 as a sifting apparatus. From this stage, in which the 

 lamellse would be two-thirds of the length of the plates of 

 baleen in the Balaenoptera rostrata, gradations, which may 

 be observed in still-existing Cetaceans, lead us onward 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 



