346 



PRACTICAL ZOOLOGY 



blooded animals in contrast to all the rest of the animals, which 

 are cold-blooded. Warm-blooded animals consume so much 

 food that a bodily temperature usually greater than that of the 

 surrounding air is maintained. This heat is the result of the 

 oxidation within the cells, and the temperature is practically 

 constant no matter how warm or cold it is outside. Feathers 

 prevent the body heat from escaping by forming many air spaces 



at the surface. The 

 temperature of the 

 bird's body ranges 

 from ioo° to 112 F., 

 whereas that of man 

 is normally only 98. 6° 

 F. 



Feathers. — How 

 wonderfully effective 

 feathers are for the 

 purposes for which 

 they are used can 

 easily be determined 

 by examining one in 

 the laboratory (Fig. 

 216). Feathers are 

 embedded in pits in 

 the skin, the feather 

 follicles. The central 

 axial rod of the feather 

 is the stem, and on 

 each side of this is a vane. The quill is that part of the stem 

 without vanes. If the vane is examined closely, it will be 

 found to consist of a great number of parallel rods, the 

 barbs. Each barb resembles in appearance an entire feather, 

 since on each side there is a row of slender projections, the 

 barbules. Hooklets are present on these barbules. These 

 hooklets hold the barbs together, and thus the entire vane 



Fig. 225. — Nest and eggs of the white-rumped 

 shrike (butcher bird). The nest was built in a 

 hawthorn tree 10 feet from the ground. (Photo. 

 by Hegner.) 



