THE MUSCLES ; THE FAT-BODY AND CCELOM. 79 



of great eminence have been led into erroneous statements when 

 they have attempted to characterise shortly a complex animal 

 mechanism which they did not think it worth while to analyse 

 completely.* 



The action of flight and the muscles attached to the wings 

 are best studied in Insects of powerful flight. The female 

 Cockroach cannot fly at all, and the male is by no means a good 

 flier. Both sexes are, however, admirably fitted for running. 



In running, two sets, each consisting of three legs, move 

 simultaneouslv. A set includes a fore and hind limb of the 



J 



same side and the opposite middle leg. Numbering them from 

 before backwards, and distinguishing the right and left sides by 

 their initial letters, we can represent the legs which work 

 toether as 



Lo Re 



L! R % 2 LS 



The different legs have different modes of action. The fore- 

 leg may be compared to a grappling-iron ; it is extended, 

 seizes the ground with its claws, and drags the body towards 

 its point of attachment. The middle leg is chiefly used to 

 support and steady the body, but has some pushing power. 

 The hind leg, the largest of the three, is effective in shoving, 

 and chiefly propels the body. 



Muscular Force of Insects. 



*^ 



The force exerted bv Insects has long- been remarked with 



KI 



surprise, and it is a fact familiar, not only to naturalists, but to 

 all observant persons, that, making allowance for their small 

 size, Insects are the most powerful of common animals. 



* For example, Prof. Huxley, in his Anatomy of Invertebrated Animals (p. 254), 

 says that "as the hard skeleton [of Arthropods] is hollow, and the muscles are 

 inside it, it follows that the body, or a limb, is bent towards that side of its axis, 

 which is opposite to that on which a contracting muscle is situated." The flexor 

 muscles of the tail of the Crayfish, which, according to the above rule, should be 

 extensors, the muscles of the mandibles of an Insect, and the flexors and extensors 

 of Crustacean pincers are among the many conspicuous exceptions to this rule. 



