40 



GENERAL ZOOLOGY 



abdomen, are here placed beneath the edge of the wing- 

 covers on the back, and the space beneath the wing-covers 

 is used as an air-reservoir, which is replenished with pure 

 air by rising to the surface. In other species a thin coating 

 of air is carried on the under side of the abdomen. This 

 supply is obtained by pushing the head above water and 

 capturing a bubble of air with the antennoe, which are quickly 

 folded beneath the head, carrying the imprisoned bubble to 

 the under surface of the body. 



Scavenger-Beetles. A useful part in the economy of nature 

 is played by the scavenger-beetles (Necroph' orus, Fig. 23), 

 large black, red-spotted insects, \vhich dig beneath the car- 

 casses of small animals, thus burying them beneath the 



surface. The female 

 then lays her eggs in 

 the decaying material, 

 upon which the larva) 

 1 feed until ready to 

 transform. This exer- 

 tion removes the car- 

 cass from the field of 

 operations of other 

 creatures which might 

 feed upon it, if it were 

 left exposed, and thus 



FIG. 23. Scavenger-Beetle. Slightly enlarged destroy the eggs, or 



larvae. As these 



beetles are protected by a fetid odor, their striking markings 

 are usually spoken of as an example of warning coloration, 

 a term applied to those appearances in animals which are 

 thought to be useful in notifying enemies of the presence of 

 something disagreeable or dangerous. 



Lady-Beetles. The common and well-known insects vari- 

 ously called lady-beetles, lady-bugs, or lady-birds (CoccineVla, 



