STRUCTURE OF INSECTS. 879 



compact and firm, and toothed in the edge, so that it 

 may form an engine for digging and cutting. 



The tarsus, or foot, varies very much, and exhibits a 

 wonderful deal of mechanical contrivance, and a very 

 nice adaptation of parts to the office that the organ has 

 to perform. There is generally, whatever may be the 

 number of joints or articulations in the part of the 

 limb, a very strong flexor or contracting muscle, by 

 means of which it is enabled to attach itself firmly to 

 any substance. 



The claw is equally varied in its structure. Some- 

 times, as in the case of the mole cricket, it is in the 

 form of a rake, for hewing down and drawing along 

 mud j at other times there are hooked claws, all bend- 

 ing in the same direction, by means of which it can 

 suspend itself; sometimes again the claws act opposite 

 to each other like a hand ; and at other times there is 

 but a single claw, to which a little protuberance on the 

 tarsus serves as a thumb. 



Such are the outlines of the merely mechanical struc- 

 ture of insects. The other parts are equally curious, 

 even those that are general to the class, and have no 

 reference to the peculiar habits of any one. The nervous 

 system, which is ramified from the brain contained in the 

 head ; the singular formation that often is displayed in 

 the mouth, which is at one time a pump, and at another 

 a pair of scissors ; the complicated contrivance of cells 

 and tubes, by which the blood is aerated ; and, above 

 all, the way in which nature has provided for the con- 

 tinuation of the species, with the long probation and 

 the singular changes through which many of them have 

 to pass before they can enjoy the day or the hour 





