THE MUSCULAR SYSTEM 211 



2. INTERNAL ANATOMY 

 THE MUSCULAR SYSTEM 



In its general arrangement the muscular system of insects corre- 

 sponds to the segmented structure of the body. Of the muscles 

 belonging to a single segment, some extend from the front edge of 

 one segment to that of the next behind it, and others to the hinder 

 edge ; there are also sets of dorsal and ventral muscles passing in an 

 oblique or vertical course (Figs. 16-18). As Lang observes, " the 

 greater part of the muscles of the body can be traced back to a paired 

 system of dorsal and ventral intersegmental longitudinal muscles." 

 The muscular system is simplest in larval insects, such as caterpillars, 

 where the musculature is serially repeated in each segment. 



In the larva of Cossus Lyonet found on one side of the body 217 

 dorsal, 154 lateral, 369 ventral, and in the thoracic legs 63, or 803 

 muscles in all. " Adding to this number the 12 small muscles of the 

 second segment, and 8 others of the third, which he did not describe, 

 there would be for all the muscles on one side of the caterpillar 823. 

 This would make for the entire body 1646, without counting a 

 small single muscle which occurs in the subdivision of the last seg- 

 ment," and also those of the internal organs as well as those of the 

 head, so that the total number probably amounts to about 2000, not 

 3000, as usually stated in the books. Lubbock admits that Lyonet 

 was right in his mode of estimating the number. In the larva of 

 Pi/gcera biicephala he found that " the large muscles scarcely vary at 

 all," though certain smaller ones are very variable. Lubbock ob- 

 served that certain of the longitudinal muscles in the caterpillar of 

 Diloba split up into numerous, not less than ten, separate fascicles. 

 "This separation of the fibres composing a muscle into separate fas- 

 cicles is carried on to a much greater extent in the larvae of Coleop- 

 tera. Of course in the imago the number of thoracic muscles is 

 greatly increased, or at least in Dyticus and the wood-feeding 

 Lamellicorns, which alone I have examined. In these two groups 

 each of the larger muscles is represented by at least twenty separate 

 fascicles, which makes it far more difficult to distinguish the ar- 

 rangement of the muscles." 



The muscles are whitish or colorless and transparent, those in the 

 thorax being yellowish or pale brown ; and of a soft, almost gelatin- 

 ous consistence. In form they are simply flat and thin, straight, 

 band-like, or in rare cases pyramidal, barrel or feather shaped. 



