328 



INTRODUCTION TO ARTHROPODS 



ma!p.t. 



-rect. 



In mosquitoes (Fig. 189) the salivary glands consist of three 

 lobes, one lobe being noticeably different in appearance and 

 secretion from the others. The pharynx connects with the 

 stomach by a slender oesophagus. Various means are used by 



blood-sucking insects to increase 

 their capacity. In the bugs 

 (Fig. 135) the stomach is ex- 

 tremely distensible and serves as 

 a storage reservoir. In fleas and 

 many biting flies there is an ex- 

 pansion of the oesophagus an- 

 terior to the true stomach, called 

 the proventriculus; in mosqui- 

 toes there are capacious pouch- 

 like food reservoirs or outgrowths 

 from the oesophagus in addition 

 to the proventriculus (Fig. 189). 

 Just behind the true stomach at 

 the beginning of the intestine 

 there open a number of long 

 slender tubes, the "Malpighian 

 tubules" (Fig. 135, malp. t.). 

 These are the excretory organs, 



FIG. 135. Digestive tract of a Re- * 



duviid bug; ace. sal. gi., accessory corresponding to the kidneys of 

 salivary gland; conn. d. connecting vertebrate animals. Their func- 



duct between salivary glands; int., in- 

 testine; malp. t., malpighian tubules; tion IS to Collect the Waste 

 CBS oesophagus; rect -.rectum; sal. gl matter o f metabolism from the 

 salivary gland. (Partly after Dufour.) 



blood and pour it into the in- 

 testine, whence it can ultimately be voided through the anus. 

 The length of the intestine varies, being usually longer in vege- 

 table-feeding insects than in carnivorous ones. It often has a 

 marked expansion, the anal pouch, at its posterior end. 



The tracheae of insects, as already intimated, are really a ven- 

 tilation system consisting of air tubes ramifying all through the 

 body even to the tips of the antennae and legs. They open by a 

 series of pores along the sides of the insect known as spiracles, 

 which function as do the nostrils of higher animals. The prin- 

 ciple of oil sprays for insects is to form a film of oil over the 

 spiracles, so that the insects will suffocate. 



The nervous system of insects is very highly developed for 



