i6 The Structure and Special Physiology of Insects 



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

 spermatheca during these after-years. 



finu-y 



-,-^^ 



FlC. 27. — Alimentary canal of dobson-fly, Cory(fa/:jcornM/<j. ^, larva; B, adult; C, pupa; 

 oes., a'sophagus; prov., provcntriculus; g.c, gastric ccEca; vent., vcntriculus; r.g., 

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

 ccccum; 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 



Fig. 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 



