. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. 328 INTRODUCTION TO ARTHROPODS 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
. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. 328 INTRODUCTION TO ARTHROPODS 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.). ^. , â These are the excretory organs, Fig. 135. Digestive tract of a Re- , . , ]â duviid bug; ace. sal. gi., accessory correspondmg to the kidneys ot salivary gland; conn, d., connecting vertebrate animals. Their func- duct between salivary glands; int., in- . n â testine; malp. t., malpighian tubules; tion IS tO COllect the waste oes., oesophagus; rect., rectum; sal. gi matter of metaboUsm from the salivary gland. (Partly after Uufour.) . . 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-
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