ENTOMOLOGY IN OUTLINE STRUCTURE OF 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 o 



FIG. 25. Alimentary tract of a grasshopper (Melanoplus differential!*), c, colon ; 

 cr, crop; gc, gc, gastric caeca ; i, ileum; m, mid intestine, or stomach; mt, Mal- 

 pighian, or kidney, tubes; o, esophagus; p, pharynx; r, rectum ; ., salivary 

 gland of left side. 



The digest ire 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 (Carabus). 

 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 caeca: 

 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; h, heart; the ar- 

 rows show direction taken by currents 

 of blood. (After Kolbe.) 



