GENERAL ANATOMY OF INSECTS 327 



of modifications. In mosquitoes the mouthparts (Fig. 191) are 

 much as in bugs, but the labrum-epipharynx and hypopharynx 

 are also modified into long piercing organs, and the latter is 

 fashioned into a true hypodermic needle for injecting salivary 

 secretions. In blackflies and tabanids (Figs. 220 and 225) the 

 parts are similar but the piercing organs are shorter and more 

 bladelike, resembling daggers rather than needles. In the 

 tsetse flies and stable-flies (Figs. 220 and 225) the lower lip itself 

 is the chief piercing organ, the labrum-epipharynx and hypo- 

 pharynx contained in it being needle-like and capable of forming 

 a sucking tube by apposition with each other. The mandibles 

 and maxillae are much reduced or rudimentary, but the maxillary 

 palpi are conspicuous, and in tsetse flies form a perfect sheath 

 for the proboscis. In the houseflies and their non-blood-sucking 

 allies the mouthparts are most modified, being all molded to- 

 gether to form a fleshy proboscis especially fitted for lapping 

 up liquid foods. In fleas the mouthparts (Fig. 178) are somewhat 

 as they are in the biting flies, but the mandibles are not modified 

 as piercing organs but as protective flaps, and the sheath for the 

 piercing organs is formed from the labial palpi instead of from 

 the labium or lower lip itself. The mouthparts of sucking lice 

 (Fig. 171) .are stiU not thoroughly understood but the piercing 

 and sucking organs, whatever parts they really represent, can 

 be retracted into a blind pouch under the pharynx. The mouth 

 parts of such insects as moths, bees, wasps, etc., are also remark- 

 able examples of structural adaptations, but they do not concern 

 us here. 



General Anatomy. — The digestive tract of insects (Fig. 135) 

 is often highly developed and differentiated. The blood-sucking 

 insects have a muscular pharynx in the head which acts like a 

 suction pump. In the bedbug, for instance, the powerful muscles 

 which are used to expand the pharynx and thereby produce 

 suction occupy a considerable portion of the inside of the head, 

 and the area on top of the head to which they are attached is 

 distinctly visible on the outside. The pair of salivary glands 

 open into the floor of the pharynx, but they themselves are 

 usually situated in the thorax. Often they are very highly de- 

 veloped. In the true bugs they have connected with them 

 accessory salivary glands, which in some species may serve at 

 least in part as storage vats for holding the secretion temporarily. 



