ANATOMY 
AND PHYSIOLOGY 
87 
The more important muscles in the body of a cockroach are 
represented in Figs. 106-108, from Miuall 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 
of insects differ 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 
muscles 
Fic. 100. 
Striated muscle fiber of 
an insect. 
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 
ETGMeTO: 
nl 
striated muscle 
trans- 
Minute structure of a 
fiber. A, longitudinal section; B, 
verse section in the region of /; C, trans- 
verse section in the region of n. I, 
longitudinal fibrille; 1, 
brane; n/, nucleus; 7, 
sarcolemma.—After JANET. 
Krause’s mem- 
radial fibrille; s, 
fibers of an insect present 
a striated appearance, owing 
to alternate light and dark 
bands (Fig. 109), the for- 
mer being singly refracting, 
or isotropic, and the latter 
doubly refracting, or aniso- 
tropic. 
The 
these fibers, being extremely 
difficult of 
has given rise to much dif- 
minute structure of 
interpretation, 
ference of opinion. The 
most plausible view is that 
of van Gehuchten, Janet 
and others, who hold that both kinds of dark bands (Fig 
110) consist of highly elastic threads of spongioplasm (aniso- 
tropic) embedded in a matrix of clear, semi-fluid, nutritive 
