372 ZOOLOGY. 



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514. The thorax of insects occupies the middle portion 

 ie body, and carries limbs and wings. It is always com- 

 posed of three circles or rings, named prothorax, meso- 

 thorax, and metathorax (a b c, Fig. 338) ; and it is to the 

 ventral arch of each of these rings that one of the pairs of 

 limbs are fixed. The wings, on the contrary, spring from 

 the dorsal arch of the thoracic rings; but the prothorax 

 (a) never carries any, and there never exists more than a 

 pair of these appendages on each of the two following rings, 

 so that there are never more than two pairs. 



Fig. 342. Notonecte. Fig. 343. Cricket. 



515. In the limbs of insects we distinguish a haunch 

 composed of two joints, a thigh, and leg, and a sort of foot 

 called tarsus, divided into several joints, the num- 

 ber of which varies from two to five. They termi- 

 nate in nails. It may be readily imagined that their 

 forms vary in unison with the habits of the animals. 

 Thus, insects which have the hinder limbs long 

 (Fig. 343), leap rather than walk. In insects 

 which swim, such as the dytiques, the notonectes 

 (Fig. 342), and the gyrin, commonly called tour- 

 Syrin ~ niquets (Fig. 344), the tarsi are generally flattened, 

 ciliated, and disposed like oars; and in those 

 which can walk on smooth surfaces with the body suspended, 

 we find on the terminal joint a sucker, by which they adhere 

 to the body they touch. Sometimes, also, the anterior limbs 

 are enlarged, as in moles, to enable them to dig into the 

 soil. The courtiliere (Fi^. 345), which does such mischief 

 by cutting the roots in its course, is an example of this 

 arrangement. 



There are also species in which these same limbs form 



