176 



A.XIMAL BIOLOGY 



shape to enable the body to penetrate the air, and a small 

 neck would destroy the conical form. The internal organs 

 are compactly arranged and rest in the cavity of the breast 

 bone. The bellows-like air sacs filled with warm air 

 lighten the bird's weight. The bones are hollow and very 

 thin. The large tail quills are used by the bird only in 

 guiding its flight up and down, or balancing on a limb. 



The feet also aid a 

 flying bird in bal- 

 ancing. The wing 

 is so constructed as 

 to present to the 

 air a remarkably 

 large surface com- 

 pared with the 

 small bony support 

 in the wing skele- 

 ton. Are tubes 

 ever resorted to by 

 human architects when lightness combined with strength 

 is desired ? Which quills in the wing serve to lengthen 

 it? (Fig. 296.) To broaden it? Is flight more difficult 

 for a bird or a butterfly ? Which of them do the flying 

 machines more closely resemble? Can any bird fly for a 

 long time without flapping its wings ? 



Fig. 322. — Herring Gull. (Order?) 



Exercise in the Use of the Key. — Copy this list and write the name 

 of the order to which each of the birds belongs. (Key, page 177.) 



Cockatoo (Fig. 320) Wren (Fig. 310) Pheasant (Fig. 319) 



Sacred Ibis (Fig. 328) Apteryx (Fig. 318) Wood Duck (Fig. 314) 



Screech Owl (Fig. 311) Lyre bird (Fig. 327) Jacana (Fig. 324) 



Nightingale (Fig. 325) Road Runner (Fig. 313) Sea Gull (Fig. 322) 



Top-knot Quail (Fig. Ostrich (Fig. 332) Heron (Fig. 315) 



329) Penguin (Fig. 330) Hawk (Fig. 312) 



