ANATOMY AND PHYSIOLOGY 



FIG. 109. 



The more important muscles in the body of a cockroach are 

 represented in Figs. 106-108, from Miall and Denny. The 

 longitudinal sternals with the longitudinal tergals act to tele- 

 scope the abdominal segments ; the oblique 

 sternals bend the abdomen laterally; the 

 tergo-sternals, or vertical expiratory mus- 

 cles, draw the tergum and sternum to- 

 gether. 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 chitinous 

 tendons. A muscle is a bundle of long 



FIG. no. 



fibers, each of which has an outer elastic striated muscle fiber of 

 membrane, or sarco lemma, 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 

 nl a striated appearance, owing 

 to alternate light and dark 

 bands (Fig. 109), the for- 

 mer being singly refracting, 

 or iso tropic, and the latter 

 doubly refracting, or aniso- 

 tropic. 



The minute structure of 

 these fibers, being extremely 



Minute structure of a striated muscle difficult of interpretation, 

 fiber. A, longitudinal section; B, trans- 

 verse section in the region of /; C, trans- has glVCn HSC to much dlf- 

 yerse section in the region of . /, ference Q f opinion. The 

 longitudinal fibrillse; n, Krause s mem- 

 brane; nl, nucleus; r, radial fibrillae; s, niOSt plausible view is that 

 sarcolemma. After JANET. , /^> 1 1 - T 



of van Gehuchten, Janet 



and others, who hold that both kinds of dark bands (Fig 

 no) consist of highly elastic threads of spongioplasm (aniso- 

 tropic) embedded in a matrix of clear, semi-fluid, nutritive 



