7 8 



ENTOMOLOGY 



those of Straus-Diirckheim (1828) on the beetle Melolontha; Lyonet 

 (1762), Newport (1834) and Lubbock (1859) on caterpillars; Lubbock 

 and Janet on Hymenoptera; Bauer (1910) on Dytiscus; and Berlese 

 (1909-13) on various insects. 



The more important muscles in the body of a cockroach 

 are represented in Figs. 108-110, from Miall and Denny. 

 The longitudinal sternals with the longitudinal tergals act 

 to telescope the abdominal segments; the oblique ster- 

 nals bend the abdomen laterally; the ter go sternals, or 

 vertical expiratory muscles, draw the tergum and sternum 

 together. The muscles of the legs and the wings have 

 already been referred to. 



Structure of Muscles. The muscles of insects differ 

 greatly in form and are inserted frequently by means of 



in. 



muscle cn itinous tendons. A muscle is a bundle of long fibers, 



ifiC-O/-** O / 



FIG. 

 Striated 

 fiber of an insect. 



each of which has an outer elastic membrane, or 

 sarcolemma, within which are several nuclei; thus the fiber represents 

 several cells, which have become confluent. With rare exceptions 

 ("alary" muscles and possibly a few thoracic muscles) the muscle fibers 

 of an insect present a striated appear- 

 ance, owing to alternate light and dark 

 bands (Fig. 1 1 1) , the former being singly 

 refracting, or isotropic, and the latter 

 doubly refracting, or anisotropic. 



The minute structure of these fibers, 

 being extremely difficult of interpreta- 

 tion, has given rise to much difference of 

 opinion. The most plausible view is 

 that of van Gehuchten, Janet and others, 



..., iii-j r j i i_ j FIG. 112. Minute structure of a 



who hold that both kinds ot dark bands striate d muscle fiber. A, longitudinal 



(Fig. 1 1 2) Consist Of highly elastic threads section; B, transverse section in the 



region of I; C, transverse section in the 



Of Spongioplasm (anisotropic) embedded region of n. I, longitudinal fibrill; 



in a matrix of clear, semi-fluid, nutritive ?VaS U fibriii^Tsar^ 

 hyaloplasm (isotropic). The spongio- JANET. 

 plasmic threads of the long bands extend 



longitudinally and those of the short bands ("Krause's membrane"} 

 radially, in respect to the form of the fiber. Moreover, the attenuated 

 extremities of the longitudinal fibrillae connect with the radial fibrillae, 

 the points of connection being marked by slight thickenings, or nodes, 

 which go to make up Krause's membrane. \ 



