and the Denticulation of the Beak of certain Birds. 109 



young gannet is fully fledged, it has no serratures on^its beak, 

 the edges of which are quite even, and that until it has flown 

 about for some time, and shifted for itself, they remain entire. 

 It is therefore evident that use has broken the edges into irre- 

 gular serratures, and that the regularity of the direction of these 

 serratures must depend upon the action, or, more probably, 

 chiefly upon the organic structure of the bill, which gives it a 

 tendency, under the application of force, to break in a particular 

 way. 



It is also a fact, a curious fact, right to the purpose, that the 

 young gannet has no serratures on its middle claw, until it has 

 left the nest and floAvn about for some time. It is therefore evi- 

 dent that use produces the serratures of the claw. But gannets 

 never employ their feet in catching fish, and the act of scratch- 

 ing their heads could never break their claws. Wherefore, the 

 serratures are produced in some other way, perhaps by the 

 weight of the bird in settling, and the action of the flexors of 

 the toes in strongly pressing the claw against the rock, where- 

 by the edge of the middle claw, the only one that is thin and 

 flexible, breaks into parallel rents. If this be the case in the 

 gannet, analogy leads us to suppose it to be equally so in the 

 heron and the goatsucker. I am not, however, inclined to run 

 into conjecture, and therefore stop at a point where one can 

 easily look back and separate fact from fancy. 



In the mean time, it would be curious to observe whether the 

 young of all birds which have irregularly serrated bills, have 

 the margins even until they leave the nest, as in the case of the 

 gannet ; and whether the middle claw of the young of such birds 

 as have that organ serrated in the adult state, is as entire as in 

 the species just mentioned. When these facts are determined, 

 and the habits of the species closely examined, we may be able 

 to discover the real nature of the serrated claw. 



With respect to the serrature of the beak, I have still to re- 

 mark, that it occurs in many birds in various degrees, but al- 

 ways and exclusively in such as have beaks with long, sharp and 

 thin edges. Thus, irregular serratures are occasionally seen in 

 the bill of the terns, and always in the same direction. They 

 are more decided and regular in the genera Sula and Phaeton. 

 In young birds of these genera, they are usually less marked, 



