106 AN INTROD UCTION TO ENTOMOLOG Y 



brates. But the muscles that move the appendages of the body- 

 are furnished with a tendon at the end farthest from the body 



(Fig. 123). 



The muscles of in- 

 sects appear very differ- 

 ently from those of Ver- 

 tebrates. In insects, the 

 Fig. 123— A leg of 'a May-beetle (After Straus- muscles are either color- 

 Durckheim). ' j^^g ^^^ transparent, or 



yellowish white; and they are soft, almost of a gelatinous consistency; 

 notwithstanding this they are very efficient. The fibers of insect 

 muscles are usually, if not always, of the striated type. 



Much has been written regarding the muscular power of insects, 

 which has been supposed to be extraordinarily great; the power of 

 leaping possessed by many and the great loads, compared to the 

 weight of the body of the insect, that insects have drawn when 

 harnessed to them by experimenters, have been cited as illustrating 

 this. But it has been pointed out that these conclusions are not 

 warranted; that the comparative contractile force of muscles of the 

 same kind depends on the number and thickness of the fibers, that is, 

 on the comparative areas of the cross-sections of the muscles com- 

 pared; that this sectional area increases as the square of any linear 

 dimension, while the weight of similar bodies increases as the cube of 

 any linear dimension ; and consequently, that the muscles of the legs 

 of an insect one fourth inch long and supporting a load 399 times its 

 own weight, would be subjected to the same stress, per square inch of 

 cross-section, as they would be in an insect 100 inches long of precisely 

 similar shape, that carried only its own weight. We thus see that it is 

 the small size of insects rather than an unusual strength of their 

 muscles, that makes possible the apparently marvelous exhibitions of 

 muscular power. 



Detailed accounts of the arrangement of the muscles in particular 

 insects have been published by various writers; among the more 

 important of these monographs are the following: Lyonet (1762), 

 on the larv^a of a cossid moth; Straus-Durckheim (1828), on a May- 

 beetle; Newport (1839), on the larva of a Sphinx moth; Lubbock 

 (1858), on the larva Pygaera hucephala; Berlese ('09a), on several 

 insects; and Forbes ('14) on caterpillars. 



