1 6 The Structure and Special Physiology of Insects 



receive several million spermatozoa at mating, and retain them alive in the 

 spermatheca during these after-years. 



int. 



FlG. 27. Alimentary canal of dobson-fly, Corydalis cornuta. A, larva; B, adult; C, pupa; 

 oes., oesophagus; prov., proventriculus; g.c., gastric cceca; vent., ventriculus; r.g., 

 reproductive gland; m.t., Malpighian tubules; int., intestine; int.c., intestinal 

 ccecum; rec., rectum; drg., oviduct. (After Leidy; twice natural size.) 



The circulatory system of insects presents two particular features of inter- 

 est in that the blood does not, as in our bodies, carry oxygen to the tissues, and 



FlG. 28. Cross-section and longitudinal section of salivary gland of giant crane-fly, 

 Holorusia rubiginosa. (Greatly magnified.) 



that there is a contractile pulsating heart-like organ, but no arteries or veins. 

 The so-called heart is a delicate- walled, narrow, subcylindrical vessel com- 

 posed of a series of most commonly from three to eight successive cham- 

 bers lying longitudinally along the median line just underneath the dorsal 

 wall of the abdomen and thorax (Figs. 30 and 31). Each chamber opens, 

 guarded by a simple valvular arrangement (Fig. 33), into the chambers 



