ENTOMOLOGY 





FIG. 



Striated muscle 

 fiber of an insect. 



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

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

 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 

 in. greatly in form and are inserted frequently by means of 

 chitinous tendons. A muscle is a bundle of long fibers, 

 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, 



i iii.Lij_-Lj_ii'j r j i i_ j FIG. 112. Minute structure of a 



who hold that both kinds of dark bands striated muscle fiber. A, longitudinal 



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



. ill! region of /; C, transverse section in the 



Of Spongio plasm (anisotropic) embedded region of n. I, longitudinal fibrillse; 



in a matrix of clear, semi-fluid, nutritive J jESStS3^=3Sf 



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 fibrill^, 



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



which go to make up Krause's membrane. 



