Chap. 30 ARTHROPODS INSECTS, SPIDERS, AND ALLIES 605 



layers of cuticle as in the blue of butterflies; or pigment and structural effects 

 may be combined in iridescence. The blackish pigment melanin and yellow 

 carotin deposited in the secretion of the outer cuticle are responsible for prac- 

 tically all chemical colors. Following the intense muscular activity of their 

 flights migratory grasshoppers, ordinarily light brown, turn dark brown with 

 orange markings. If such grasshoppers are captured and kept quiet for a 

 time their original color returns; if they are restless and continually fluttering, 

 the dark background and orange marks remain. 



Internal Structures and Functions. Body Cavity. The body cavity of in- 

 sects lacks the epithelial lining of a true coelom as in the frog. It contains 

 circulating blood and is correctly called a hemocoel. 



Muscles. The muscles of insects are complicated and numerous. In man 

 there are 792 distinct muscles, in a grasshopper over 900. The ends of insect 

 muscles are attached by tendons to knobs on the inner surface of the cuticle. 



Digestion and Assimilation of Food. The digestive tube runs an almost 

 straight course from mouth to anal opening (Fig. 30.14). In the head it is held 



casthk; caicac ovarian tubulcs 



BURSA 

 COrULATRIX 



' SALIVARY 

 'v DUCT , 

 ClRCUMlSORHAOtAl.;^; N STOMOOiAl 



COMUrSSURI ; LABIUM ^^ *'"'' saLPVARY JRD "MORACIC i^^"' MiSINTIRON maL^IGHIAN "-lUM 



MYPOmARYNX SUBISORHAMAI ^^j,^o GANGLION NERVE CO«D <IH ABDOMINAL TUBULES 



GANGLION GANGLION 



Fig. 30.14. Internal organs of the female grasshopper. The foregut extends from 

 the mouth to the openings of the stomach pouches (gastric caeca); the midgut 

 (stomach or mesenteron) from the gastric caeca to the Malpighian tubules; the 

 hindgut from the tubules to the anal opening. (Courtesy, Matheson: Entomology, 

 Ithaca, N.Y., Comstock Publishing Co., 1944.) 



in place by muscles attached to the body wall, but elsewhere it is supported by 

 the tracheae. The foregut is lined with cuticle continuous with the outer cover- 

 ing of the body; the hindgut is likewise lined; the midgut has no chitinous 

 lining. The muscular action in the walls of each region results in the churning 

 movements similar to those in other digestive tubes. 



Foregut. The foregut begins with the mouth cavity which receives the 

 saliva, continues into the curved pharynx and short esophagus that widens 

 into the thin-walled crop, then narrows into the thicker-walled gizzard. The 

 mandibles and maxillae cut and shred the food while the saliva is mixed with 

 it. The brown "molasses" extruded from the mouth when a grasshopper is 

 handled is at least partly a regurgitation from the crop mixed with fluid from 

 the gastric caeca. 



