814 THE ORIGIN OF SPECIES 



great break, as* far as fitness for sifting is concerned, 

 through the beak of the Merganetta armata, and in some 

 respects through that of the Aix sponsa, to the beak of 

 the common duck. In this latter species, the lamellae are 

 much coarser than in the shoveller, and are firmly at- 

 tached to the sides of the mandible; they are only about 

 60 in number on each side, and do not project at all 

 beneath the margin. They are square-topped, and are 

 edged with translucent hardish tissue, as if for crushing 

 food. The edges of the lower mandible are crossed by 

 numerous fine ridges, which project very little. Although 

 the beak is thus very inferior as a sifter to that of the 

 shoveller, yet this bird, as every one knows, constantly 

 uses it for this purpose. There are other species, as I 

 hear from Mr. Salvin, in which the lamellae are consider- 

 ably less developed than in the common duck; but I do 

 not know whether they use their beaks for sifting the 

 water. 



Turning to another group of the same family. In the 

 Egyptian goose (Chenalopex) the beak closely resembles 

 that of the common duck; but the lamellae are not so 

 numerous, nor so distinct from each other, nor do they 

 project so much inward; yet this goose, as I am informed 

 by Mr. E. Bartlett, "uses its bill like a duck by throwing 

 the water out at the corners." Its chief food, however, 

 is grass, which it crops like the common goose. In this 

 latter bird, the lamellae of the upper mandible are much 

 coarser than in the common duck, almost confluent, about 

 27 in number on each side, and terminating upward in 

 teeth-like knobs. The palate is also covered with hard 

 rounded knobs. The edges of the lower mandible are 

 serrated with teeth much more prominent, coarser, and 



