ORIGIN AND CHARACTERISTICS 43 



recurved like that of an Avocet ; another singu- 

 lar modification is presented in. the much-com- 

 pressed bill of birds in the genera Heliothrix 

 and Schistes. In some species the bill is hooked 

 and the edge of the mandible serrated. Amongst 

 the more aberrant types of bill mention may be 

 made of that of the Whale-headed Stork and the 

 Boat-bill (Cancroma) and Shoe-bill (Balaeniceps), 

 in which the bill is shoe or boat shaped ; of the 

 very curious bill of the Whalebirds (Prion), in 

 which the jaws do not completely close ; of the 

 bill of the Skimmer (Rhynchops), which is 

 scissor-shaped, much compressed laterally, and 

 the lower mandible is considerably longer than 

 the upper one. Mention may also be made of 

 the curiously modified bill of the Flamingoes, in 

 which the upper mandible is not only highly 

 mobile, but is much smaller than the lower one, 

 which is almost immovable ; and lastly, of the 

 singular formation of the bill of the Crossbills, 

 which, as the name of the birds indicates, has the 

 two mandibles obliquely crossed. 



We now pass to a very brief sketch of some 

 of the internal organs of a bird. Here again the 

 various divisions of the internal structure are 

 each so complicated and important that anything 

 like an exhaustive description is impossible 



