Cuap. VII.] THEORY OF NATURAL SELECTION. 183 



jaw, of about 300 plates or laminse, 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, according to Scoresby, four feet, in another three, in 

 another eighteen inches, and in the Balasnoptera 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 development?" In answer, it may 

 be asked, why should not the early progenitors of the whales with 

 baleen have possessed 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 misconstrued 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 beau- 

 tiful and complex structure than the mouth of a whale. The upper 

 mandible is furnished on each side (in the specimen examined by 

 me) with a row or comb formed of 188 thin, elastic lamellas, 

 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 membrane 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 lamellse. 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 project inwards, 

 instead of straight downwards. The entire head of the shoveller, 

 though incomparably less bulky, is about one-eighteenth of the 



