INTERNAL ANATOMY OF INSECTS. 177 



appeared to be twisted spirally 3 . In spiders the muscles 

 seemed to him to consist of two 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 g . Un- 



3 Lyonet Anat. t. iv./. 3. b Ibid. 93. 



c Cuv. Anat. Camp. i. 134. 

 d Chabrier Sur le Vol des Ins. c. i. 445. 

 e PLATE XXI. FIG. 6. a. 



f De Geer iv. /, xv./. 11. m , <t p. * Lyonet Anat. 93. 



VOL. IV. N 



