

ANATOMY AND PHYSIOLOGY 



77 



The silk glands of caddis worms (Trichoptera) are essentially like 

 those of caterpillars (Lepidoptera) but the glands of Neuroptera 

 (Chrysopa, Myrmeleon, etc.) Coccinellidae, Chrysomelidae and Syrphidse, 

 which open into the rectum, are morphologically quite different from 

 those of Lepidoptera. 



3. MUSCULAR SYSTEM 



The number of muscles possessed by an insect is surprisingly large. 

 A caterpillar, for example, has about two thousand. 



The muscles of the trunk are segmentally arranged most evidently 



adc 



ef - 



abc 



FIG. 108. FIG. 109. FIG. no. 



Muscles of cockroach; of ventral, dorsal and lateral walls, respectively, a, alary muscle; 

 abc, abductor of coxa; adc, adductor of coxa; ef, extensor of femur; h, head muscles; Is, 

 longitudinal sternal; It, longitudinal tergal; Ith, lateral thoracic; os, oblique sternal; ol, 

 oblique tergal; ts, tergo-sternal; ts 1 , first tergo-sternal. After MIALL and DENNY. 



so in the body of a larva or the abdomen of an imago, where the muscu- 

 lature is essentially the same in several successive segments. In the 

 thoracic segments of an imago, however, the musculature is, at first 

 sight, unlike that of the abdomen, and in the head it is decidedly 

 different; though future studies will doubtless show that the thoracic 

 and cephalic kinds of musculature are only modifications of the simpler 

 abdominal type modifications brought about in relation to the needs 

 of the legs, wings, mouth parts, antennae and other movable structures. 

 The muscular system has been generally neglected by students of 

 insect anatomy ; the only comprehensive studies upon the subject being 



