INTERNAL ANATOMY OF INSECTS. 181 



endless and unprofitable labour. As larva, except those 

 whose metamorphosis is semicomplete a , differ widely in 

 their system of muscles from perfect insects, I shall be- 

 gin my observations with them. 



We owe by far the most accurate and detailed ac- 

 count of the muscles of larvae to the illustrious Lyonet, 

 who, with incredible labour and patience without ex- 

 ample, dissected the caterpillar of the Cossus, and has 

 described every air-vessel, every nerve, and every mus- 

 cle that could be detected by the microscope. Cuvier 

 also has given a description of the muscles not only of 

 caterpillars, but of the larvae of the Lamellicorn beetles, 

 the Hydropliili) and the Capricorn beetles 5 . From these 

 sources are derived what I have now to lay before you. 

 If you look at one of Lyonet's plates c , the layers of 

 longitudinal muscles look like so many parallel ribands, 

 others run in an oblique, and others again in a trans- 

 verse direction d . He divides them into dorsal, ventral, 

 and lateral muscles 6 , terms which sufficiently explain 

 themselves. Of the longitudinal muscles there are four 

 principal rows f , the others are more numerous. The 

 principal object of these muscles, which are flexors and 

 extensors, is to shorten or lengthen the body, or to act on 

 any particular segment as the circumstances of the ani- 

 mal may require. I shall not here notice the muscles 

 of the head and legs, as they are not remarkably differ- 

 ent from those of perfect insects. The prolegs are moved 

 by two muscles the anterior one covering in part the 

 posterior of a remarkable structure : one of their points 



a VOL. I. p. 67. b Anat. Comp. i. 432. 



c Anat. t. vii./. 2. left hand. d Ibid, right hand. 



n Ibid. 115 . i Cuv, ubi supr. 



