ANATOMY AND PHYSIOLOGY 



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 iergals act to tele- 

 scope the abdominal segments ; the oblique 

 sternals bend the abdomen laterally; the 

 t ergo- 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. 109. 



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 



FIG. no. 



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 

 difficult of interpretation, 



erse section in the region of /; C, trans- has given HSC to miicll dif- 



ference of opinion. The 

 most plausible view is that 

 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 



Minute structure of a striated muscle 

 fiber. A, longitudinal section; B, trans 



verse section in the region of n. I, 

 longitudinal fibrillse; n, Krause's mem- 

 brane; nl, nucleus; r, radial fibrillae; s, 

 sarcolemma. After JANET. 



