THE BILL. 157 



These characters of the tomia belong to bills as 

 well as to beaks, though bills have in many instances 

 additional characters, such as being serrated, some- 

 times with little teeth reflected backwards along the 

 whole line of their margins, and at other times with 

 small transverse channels, or furrows, along a certain 

 breadth at the margin. The first of these descrip- 

 tions belongs principally to birds which dart upon 

 fish, or other slippery prey ; and the latter to those 

 which dabble in the sludge, and, as it were, sift the 

 water and mud from their food by means of the 

 channels. The former are generally hard in their 

 consistency, so that they may penetrate and retain 

 their hold like barbs ; the latter are more frequently 

 soft and flexible, and there is reason to believe that 

 they are endowed with sensation, by means of which 

 they can distinguish the food from other substances, 

 and thus retain the one and reject the other. 



Bills are, however, of so many forms, and so dif- 

 ferent in the texture of their substance, that no general 

 definition can be made descriptive of them. If om- 

 nivorous, they are generally stout, sharp at the tip, 

 and with ridges on the culmen, or centre of the upper 

 mandible, and also often at the tomia of both ; and 

 these ridges, which render the bill much stronger 

 and stiffer than if the same quantity of horny matter 

 were equally distributed over the entire surface, often 

 give a quadrangular form to the section of the bill. 

 Bills which dig into the bark or wood of trees, into 

 hard ground, or into other substances which offer 

 considerable resistance, are also provided with ridges. 

 This is the case with even those very small bills which 

 pick minute insects and larvae from the crevices of 

 bark, and thus such bills are often much stronger than 

 others, which, having a larger diameter, look more 



