¥70 INTERNAL ANATOMY OF INSECTS. 
and under a good magnifier, appeared to be twisted 
spirally*. In spiders the muscles seemed to him to 
consist of fwo substances, the one soft and the other 
hard, the last forming a kind of stiff twisted filament”. 
A muscle thus composed of different bundles of fibres 
may be stated as to its parts, in insects, to consist of 
base, middle, and apex: the base is that part by which 
they are fixed to any given point of the internal sur- 
face of the crust, or of one of its processes, which 
serves as their fulcrum; the ape is that part by which 
they are fixed, either mediately or immediately, to the 
organ to be moved; and the mzddle is the remainder of 
the muscle. We usually discover in them no inflation of 
the middle corresponding with the delly of the muscles 
in vertebrate animals; they occasionally, however, ter- 
minate in a zendon, as those of the thighs and legs; but 
these tendons are of a different nature from the fibrous 
ones of warm-blooded animals; for they are hard, elastic, 
and without apparent fibres : the fleshy ones of the mus- 
cle envelope them, and are inserted in their surface‘. 
iii. Shape. The muscles of insects are usually linear, 
with parallel sides; some are cylindrical, as those of the 
wings of the Lzbellulina*; and others, as those that 
move the legs in the caterpillar of the Cossus, are trian- 
gular*. In the suctorious mandibles of the grub of a 
common water-beetle* they are penniform, or shaped 
like a feather ; and some in the Cossus are forked’. Un- 
4 Lyonnet Anat. t. iv. f. 3. » Ibid. 93—. 
Cuv. Anat. Comp, 1. 134. 
Chabrier Sur le Vol des Ins. c. i. 445. 
Puate XXI. Fic. 6. a. * De Geer iv. ¢. xv. f. 11. mn, op 
Lyonnet Anat. 93. 
D) t.) a o 
