ENTOMOLOGY IN OUTLINE — STRUCTURE OP INSECTS. 



23 



THE INTERNAL ORGANS. 



Having now given a short account of the external organs of insects, 

 we will glance at their internal organs, which comprise a digestive, cir- 

 culatory, respiratory, and nervous system. 



/ gc m 



— ■ ''• 



FIG. 25. Alimentary tract of a grasshopper (Melanoplus diffcrnitialis). c, colon ; 

 cr, crop; gc, gc, gastric cteca : i, ileum; in, mid intestine, or stomacli; mt, Mal- 

 pighian, or kidney, tubes; n, esophagus; p, pharynx; r, rectum; s, salivary- 

 gland of left side. 



The digestire organs consist, as in the higher animals, of a contin- 

 uous tube, somewhat longer than the body, varying in form with differ- 

 ent insects, from a simple tube in 

 the Thysanura, to a complicated 

 system in the higher orders. It 

 is usually supplied with a crop, 

 gizzard, stomach, and necessary 

 assimilative organs. The diges- 

 tive tube is divided into three 

 parts : the large intestine, the 

 small intestine, and the rectum. 



FIG. 26. Digestive system of a beetle (Carabufs). 

 a, anal gland; c (of fore gut), crop; c (of hind 

 gut), colon, merging into rectum; d, evacu- 

 ating duct of anal gland; g, gastric caica; 

 i, ileum ; m, mid intestine ; mt, Malpighian 

 tubes; o, esophagus; p, proventriculus; r, res- 

 ervoir. (After Kolbe.) 



FIG. 27. Diagram to indicate the course 

 of blood in the nymph of a dragon-fly 

 {Epitheca). a, aorta ; /), heart ; the ar- 

 rows show direction taken by currents 

 of blood. (After Kolbe.) 



