16 The Structure and Special Physiology of Insects 
receive several million spermatozoa at mating, and retain them alive in the 
spermath.eca during these after-years. 
Fig. 27.— Alimentary canal of dobson-fly, Corydalis cornuta. A, larva; B, adult; C, pupa; 
oes., oesophagus; prov., proventriculus; g.c., gastric coeca; vent., ventriculus; r.g., 
reproductive gland; m.t., Malpighian tubules; int., intestine; int.c., intestinal 
coecum; 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 
