MUSCULAR SYSTEM OF INSECTS. 309 



(810.) Let the reader, therefore, imagine for an instant that great 

 law of nature, which restricts the dimensions of an insect within certain 

 bounds, dispensed with even in a single species. Suppose the Wasp or 

 the Stag-beetle dilated to the bulk of a tiger or of an elephant cased 

 in impenetrable armour furnished with jaws that would crush the solid 

 trunk of an oak winged, and capable of flight so rapid as to render 

 escape hopeless ; what would resist such destroyers ? or how could the 

 world support their ravages ? 



(811.) Such is the comparative strength of insects. Let us now pro- 

 ceed to examine the muscles to which it is owing, their structure and 

 general arrangement. 



(812.) The muscles consist of bundles of delicate fibres, that arise 

 either from the inner surface of the segments composing the skeleton, or 

 else from the internal horny septa which project into the thorax. The 

 fibres themselves are of a white or yellow colour ; and so loosely are 

 they connected by cellular tissue, that they may be separated by the 

 slightest touch. 



(813.) All the muscles of an insect may be arranged in two great 

 divisions : the first including those that unite the different segments of 

 the body ; the second, those appropriated to the movements of the limbs, 

 jaws, and other appendages. The former are entirely composed of fleshy 

 fibres ; the latter are provided with tendinous insertions, by which their 

 force is concentrated and made to act with precision upon a given point 

 of the skeleton. 



(814.) The connecting muscles are generally arranged in broad parallel 

 bands, arising from the inner surface of a given segment, and passing 

 on to be inserted in a similar manner into another segment, so that by 

 their contraction the cavity in which they are lodged is diminished by 

 the approximation of the different rings : these have no tendons. 



(815.) The locomotive muscles, of course, take their character from 

 the joints of the limb upon which they act ; and as we have already 

 seen that these movements are generally confined to those of a hinge, 

 the muscular fasciculi may be conveniently grouped into two great 

 classes the flexor muscles, that bend the joint, and the extensors, by 

 which it is again straightened, and brought back to its former position. 

 This simple arrangement will be best understood by an inspection 

 of fig. 154, representing the muscles of the leg of a Cockchafer (Melo- 

 lontha vulgar is), as they are depicted by Straus-Durckheim*. In the 

 thigh, for example, there are two muscles, one of which bends, the other 

 straightens, the tibia. The flexor (fig. 154, a) arises from the lining 

 membrane of the femur, and is inserted by a tendon into a process 

 of the tibia in such a manner as to flex the leg upon the thigh ; while 

 its antagonist (6), attached to a process derived from the other side of 



* Considerations generates sur 1'Anatomie comparee des Animaux articules, aux- 

 quelles on a joint 1'Anatomie descriptive du Hanneton. 1 vol. 4to. Paris, 1828. 



