INTERNAL ANATOMY OF INSECTS. 181 
endless and unprofitable labour. As larvcc, except those 
whose metamorphosis is semicomplete a , differ widely in 
their system of muscles horn perfect inserts, I shall be- 
gin my observations with them. 
We owe by far the most accurate and detailed ac- 
count of the muscles of larvee 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 Hydrophili, and the Capricorn beetles . From these 
sources are derived what I have now to lay before you. 
If you look at one of Lyonet's plates , 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 e , terms which sufficiently explain 
themselves. Of the longitudinal muscles there axe 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 prologs are moved 
by two muscles — the anterior one covering in part the 
posterior — of a remarkable structure: one of their points" 
3 Vol. I. p. 67. '' Anat. Comp. i. 432—. 
r Anat. t. \\\.f. 2. left hand. d Ibid, right hand. 
' Ibid, 115 — . f Cuv. ubi supr. 
