SOME SUGGESTIONS FOft BIRD STUDY. 



105 



other ? We cannot with the naked eye see what the 

 arrangement is, but from the result, i.e. a coherent web, 

 we must conclude that the barbules are hooked and that 

 the hooks of adjacent 

 barbs are linked together 

 (Fig. 29). 



Note how by pulling 

 gently the hooks release 

 their hold and the feather 

 tears. Note also how we 

 may imitate the action of ^ 



^ 



Ml 



Fig. 29. Diagram of barbs and barbulea 

 with hooks. 



the bird when it draws 



the feather through its 



bill and relinks the hooks 



again. We may do this 



by passing the severed 



part between the thumb 



and forefinger, when it will be found that the feather 



can be repaired. 



Other External Features of Note. 



Sill. Birds are toothless, but it may interest the pupils 

 to learn that this was not always so. A further reference 

 to Arcliaeopteryx, which was toothed, may be made, or to 

 Hesperornis, a North American toothed fish-eating bird, 

 long since extinct. The function of the lost teeth is in 

 part fulfilled by the horny sheath which covers both upper 

 and lower jaw. Some note should be made of adaptations 

 in the bill to different types of diet. That of the Hawks, 

 e.g. is strong, sharp-edged, notched, and hooked (Fig. 30), 

 suited for the tearing and cutting of flesh. Other types 

 which might be noted in relation to the principal items of 

 diet are, e.g., those of the finches and similar birds, short 

 and conical, or of insect-eating birds Jike swallow and 

 swift, short and broad, or broad and flat as in the ducks, 

 and so on. 



Nostrils. These are small openings near the base of the 

 bill. In the pigeon they are slit-like. 



