198 THE FOUNDATIONS OF ZOOLOGY 



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 Balcenoptera rostrata only about nine 

 inches in length. 



" With respect to the baleen, Mr. Mivart remarks that if it 

 had once attained such a size and developtnerit as to be at all 

 usefiily the7t its presei'vation and augmentation within serviceable 

 limits would be promoted by nattiral selection alone. But how to 

 obtain the beginning of such useful development? 



"In answer it may be asked, why should not the early pro- 

 genitors of the whales with baleen have possessed a mouth con- 

 structed something like the laminated beak of a duck.? Ducks, 

 like whales, subsist by sifting the mud and water; and the fam- 

 ily has sometimes been called the Cribratores, or sifters. I hope 

 I may not be misconstrued into saying that the progenitors of 

 whales did actually possess mouths laminated 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 laminae by finely graduated steps, each 

 of service to its possessor. 



" The beak of a shoveller-duck {^Spatula clypeatd) 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 laminae 

 obliquely bevelled so as to be pointed, and placed transversely to 

 the long 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 largest, being about one-third 

 of an inch in length, and they project fourteen-hundredths of an 

 inch beneath the edge. At their bases there is a short subsidiary 

 row of oblique transverse laminae. 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 Balcejiopiera rostrata, in 

 which species the baleen is only nine inches long, so that if we 



