Chap. VII.] THEOEY OF NATURAL SELECTION. 285 



species are the most apt to vary, whilst the generic 

 characters, or- those common to all the species, are the 

 most constant. 



The Greenland whale is one of the most wonderful 

 animals in the world, and the baleen, or whale-bone, one 

 of its greatest peculiarities. The baleen consists of a 

 row, on each side, of the upper jaw, of about 300 plates 

 or laminae, which stand close together transversely to 

 the longer axis of the mouth. Within the main row 

 there are some subsidiary rows. The extremities and 

 inner margins of all the plates are frayed into stiff 

 bristles, which clothe the whole gigantic palate, and 

 serve to strain or sift the water, and thus to secure the 

 minute prey on which these great animals subsist. The 

 middle and longest lamina in the Greenland whale is 

 ten, twelve, or even fifteen feet in length ; but in the 

 different species of Cetaceans there are gradations in 

 length ; the middle lamina being in one species, accord- 

 ing to Scoresby, four feet, in another three, in another 

 eighteen inches, and in the Balamoptera rostrata only 

 about nine inches in length. The quality of the whale- 

 bone also differs in the different species. 



With respect to the baleen, Mr. Mivart remarks that 

 if it " had once attained such a size and development as 

 to be at all useful, then its preservation and augmenta- 

 tion within serviceable limits would be promoted by 

 natural selection alone. But how to obtain the beginning 

 of such useful development ? " In answer, it may be 

 asked, why should not the early progenitors of the whales 

 with baleen have possessed a mouth constructed some- 

 thing like the lamellated beak of a duck ? Ducks, like 

 whales, subsist by sifting the mud and water ; and the 



