INTERNAL ANATOMY OF INSECTS. 177 
appeared to be twisted spirally a . In spiders the muscles 
seemed to him to consist of tvoo substances, the one soft 
and the other hard, the last forming a kind of stiff 
twisted filament 5 . A muscle thus composed of differ- 
ent 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 surface of the crust, or of one of its pro- 
cesses, which serves as their fulcrum ; the apex is that 
part by which they are fixed, either mediately or imme- 
diately, to the organ to be moved ; and the middle is 
the remainder of the muscle. We usually discover in 
them no inflation of the middle corresponding with the 
belly of the muscles in vertebrate animals ; they occa- 
sionally, however, terminate in a tendon, as those of the 
thighs and legs; but these tendons are of a different na- 
ture from the fibrous ones of warm-blooded animals ; 
for they are hard, elastic, and without apparent fibres : 
the fleshy ones of the muscle envelope them, and are 
inserted in their surface c . 
iii. Shape. The muscles of insects are usually linear, 
with parallel sides ; some are cylindrical, as those of the 
wings of the Libellulina d ; and others, as those that 
move the legs in the caterpillar of the Cossus, are trian- 
gular e . In the suctorious mandibles of the grub of a 
common water-beetle f they are penniform, or shaped 
like a feather ; and some in the Cossus are forked e . Un- 
a Lyonet Anat. t. iv./. 3. h Ibid. 93—. 
L ' Cuv. Anat. Comp. i. 134. 
d Chabrier Sur le Vol des Ins. c. i. 445. 
' Plate XXI. Fie. 6. a. 
1 Dc Geer iv. /. xv./. 11. m n, o p. ,! Lyonet Anat. 93. 
VOL. IV. N 
