THEORY OF NATURAL SELECTION. 205 



beak we may proceed (as I have learned from information 

 and specimens sent to me by Mr. Salvin), without any great 

 break, as far as fitness for * A fting 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 coarsei 

 than in the shoveller, and are firmly attached to the sides 

 of the mandible ; they are only about fifty 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 a 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 considerably 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 numer- 

 ous, 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 twenty-seven in num- 

 ber 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 sharper than in the duck. 

 The common goose does not sift the water, but uses its beak 

 exclusively for tearing or cutting herbage, for which purpose 

 it is so well fitted that it can crop grass closer than almost 

 any other animal. There are other species of geese, as I 

 hear from Mr. Bartlett, in which the lamellae are less devel- 

 oped than in the common goose. 



We thus see that a member of the duck family, with a 

 beak constructed like that of a common goose and adapted 

 solely for grazing, or even a member with a beak having 

 less well developed lamellse, might be converted by small 

 changes into a species like the Egyptian goose — this, into 



