CHAP. VII.] THEORY OF NATURAL SELECTION. 171 



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 1 " 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 

 beautiful 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 

 lamellae, obliquely bevelled so as to be pointed, and placed trans- 

 versely 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 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 project 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 moderately 

 large Balaenoptera rostrata, in which species the baleen is only 

 nine inches long ; so that if we were to make the head of the 

 shoveller as long as that of the Balaenoptera, the lamellae would 

 be six inches in length, that is, two-thirds of the length of the 

 baleen in this species of whale. The lower mandible of the 

 shoveller-duck is furnished with lamellae of equal length with 

 those above, but finer ; and in being thus furnished it differs 

 conspicuously from the lower jaw of a whale, which is destitute 

 of baleen. On the other hand, the extremities of these lower 

 lamellae are frayed into fine bristly points, so that they thus 

 curiously resemble the plates of baleen. In the genus Prion, a 

 member of the distinct family of the Petrels, the upper mandible 

 alone is furnished with lamellae, which are well developed and 

 project beneath the margin ; so that the beak of this bird resem- 

 bles in this respect the inouth of a whale. 



