142 A COURSE ON ZOOLOGY. 



firmly on leaves and branches from which it would other- 

 wise be shaken by the lightest breeze. 



To the thorax are likewise attached the organs by 

 whose aid the beetle transports itself through the air. 

 Some insects, much fewer than the others, have no wings; 

 some, such as the house-fly, have two ; others, such as 

 the bee, the dragon-fly, and the beetle, have four. But 

 while the four wings of the dragon-fly are flexible, thin, 

 and transparent like gauze, in the beetle two are hard 

 and horny, and serve only in fact as covers for the other 

 two. The latter are very delicate, very fragile, and much 

 larger, and during repose they are folded up and pro- 

 tected beneath their covers. The hard wings are called 

 elytra, sheaths, or wing-cases. 



The membranous wings are attached to the meso- 

 thorax, and the elytra are fixed to the metathorax. The 

 prothorax is designated more particularly as the corselet, 

 and carries only the first pair of legs and the dorsal ap- 

 pendages. This segment is very largely developed in its 

 dorsal part, and forms the greater part of the thorax ; the 

 remainder is concealed by the wings. 



Insects differ from animals having an interior skeleton 

 not only by the inverse arrangement of their hard and soft 

 parts: the whole organization presents profound modi- 

 fications which we must study. 



The digestive apparatus includes an oesophagus, then 

 an enlargement or gizzard, followed by a stomach 

 studded with pepsin glands. Then comes the intestine, 

 more or less lengthy and coiled. There is no liver; 

 three pair of coiled tubes open into the intestine at its 

 junction with the stomach, and appear to fill at the same 

 time the functions of liver and of urinary apparatus. 

 They are called Malpighian tubes. 



