THEORY OF NATURAL SELECTION 237 



four feet, in another three, in another eighteen inches, and in 

 the Balaenoptera 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 augmentation within 

 serviceable limits would be promoted by natural selection 

 alone. But how to obtain the beginning of such useful de- 

 velopment?" In answer, it may be asked, why should not 

 the early progenitors of the whales with baleen have pos- 

 sessed a mouth constructed something like the lamellated 

 beak of a duck? Ducks, like whales, subsist by sifting the 

 mud and water; and the family has sometimes been called 

 Criblatores, or sifters. I hope that I may not be miscon- 

 strued into saying that the progenitors of whales did actually 

 possess mouths lamellated like the beak of a duck. I wish 

 only to show that this is not incredible, and that the immense 

 plates of baleen in the Greenland whale might have been 

 developed from such lamellae by finely graduated steps, each 

 of service to its possessor. 



The beak of a shoveller-duck (Spatula clypeata) is a more 

 beautiful and complex structure than the mouth of a whale. 

 The upper mandible is furnished on each side (in the speci- 

 men examined by me) with a row or comb formed of i88 

 thin, elastic lamellae, obliquely bevelled so as to be pointed, 

 and placed transversely to the longer axis of the mouth. 

 They arise from the palate, and are attached by flexible mem- 

 brane to the sides of the mandible. Those standing towards 

 the middle are the longest, being about one-third of an inch 

 in length, and they project -14 of an inch beneath the edge. 

 At their bases there is a short subsidiary row of obliquely 

 transverse lamellae. In these several respects they resemble 

 the plates of baleen in the mouth of a whale. But towards 

 the extremity of the beak they differ much, as they pro- 

 ject inwards, instead of straight downwards. The entire 

 head of the shoveller, though incomparably less bulky, is 

 about one-eighteenth of the length of the head of a mod- 

 erately large Balsenoptera rostrata, in which species the 

 baleen is only nine inches long; so that if we were to make 



