00 TRANSFORMATIONS OF THE 



skin, have increased so as to fill more than half of 

 the interior ; the oblique muscles occupy almost 

 all the rest, and both sets retain nearly the same 

 direction as in the larva. These muscular bun- 

 dles, through which the alimentary canal, the 

 dorsal vessel, and the nervous cord seem now 

 scarcely able to find passage, are the muscles of 

 flight ; and yet they touch neither the wings nor 

 their attachments. The flight of butterflies is 

 mainly effected simply by changes in the form of 

 the thorax, produced by the contraction of one or 

 the other set of muscles ; the longitudinal mus- 

 cles, which are the more voluminous, serving to 

 shorten and elevate the thorax, and so depress the 

 wings, while the oblique muscles serve to lengthen 

 and depress the thorax and elevate the wings. 

 The changes that have occurred in the muscular 

 system are due to degeneration and reorganization 

 during pupal life ; even where, as in the longitu- 

 dinal muscles of the thorax, the direction is the 

 same, it should be noticed that they now reach 

 across the second and third thoracic segments 

 without interruption, whereas in the caterpillar 

 they were formed of distinct muscles, each of 

 which crossed only a single segment, though with 

 contiguous ends. 



Transformations have also occurred in the 

 digestive system, and these changes commence in 

 the very earliest stages of pupal life and continue 



