310 



INSECTA. 



Fig. 154. 



the joint, has an opposite effect, and by its contraction extends the leg. 



In the tibia there are likewise two muscles, so 



disposed as to move the entire tarsus and foot. 



The extensor (/) of the tarsns is the smallest ; 



it arises from the lower half of the interior of 



the tibia, and is inserted into the margin of the 



first joint of the tarsus : bnt the flexor of the 



foot (c), arising from the upper half of the 



cavity of the tibia, ends in a delicate tendon, 



which passes through all the tarsal segments, to 



be fixed to the flexor tendon of the claw-joint, 



upon which it acts ; and as it traverses the 



penultimate joint it receives the fibres of an 

 accessoiy muscle (d). The extetisor of the claw 

 (0) is likewise placed in the penultimate tarsal 

 segment, and strikingly exhibits, by its small 

 comparative size, the feebleness of its action 

 when compared with that of the flexors of the 

 same joint. 



(816.) It would be superfluous to describe 

 more in detail the disposition of individual 

 muscles, as the above example will abundantly 

 suffice to give the reader an idea of the general 

 arrangement of the muscular system, not in 

 insects only, but in all the ARTICULATA pro- 

 vided with jointed extremities. 



(817.) The substances employed as food by 

 insects are various, in proportion to the exten- 

 sive distribution of the class. Some devour the 

 leaves of vegetables, or feed upon grasses and succulent plants ; others 

 destroy timber, and the bark or roots of trees ; while some, more deli- 

 cately organized, are content to extract the juices of the expanding buds, 

 or sip the honeyed fluids from the flowers. Many tribes are carnivo- 

 rous in their habits, armed with various weapons of destruction, and 

 carry on a perpetual warfare with their own or other species ; and again, 

 there are countless swarms appointed in their various spheres to attack 

 all dead and putrefying materials, and thus to assist in the removal of 

 substances which, by their accumulation, might prove a constant source 

 of annoyance and mischief. Such differences in the nature of their food 

 demand, of course, corresponding diversity in the construction of the in- 

 struments employed for procuring nourishment ; and accordingly we find, 

 in the structure of the mouths of these little beings, innumerable modifi- 

 cations adapting them to different offices. The mouths of all creatures 

 are constructed upon purely mechanical principles ; and in few classes of 

 the animal world have we more beautiful illustrations of design and con- 



Muscles of the leg of a 

 Cockchafer. 



