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176 INSECTS. 



and the fragments of other plants ; the largest European species (Psocus lineatus) 

 being scarcely more than a quarter of an inch long. 



The Mallophaga, commonly known as bird-lice, are small wingless 

 Bird-Lice. ,.* ,. ,. ' , , , ,.. . 



insects, resembling ordinary lice to some extent, but differing from them 



in many characters, and especially in the structure of the mouth, which is fitted 

 for taking food by biting instead of sucking. They form a distinct group, now 



generally placed in the Pseudoneuroptera, though 

 some entomologists assign it a position near the 

 Pediculina or true lice. The bird-lice are flat- 

 bodied insects, with a broad head, varying a good 

 deal in form, and a thorax which usually appears 

 to consist of only two segments. Their antennae 

 are short and composed of three, four, or five 

 joints; and their eyes, when present, are simple. 

 The mandibles appear as short hooks, sometimes 

 toothed on the inner side ; the maxillae are short 



Psocus lineatus (enlarged three times). 



and said to be always palpless; while the lower 



lip is distinct and often bears palpi. The legs are short and stout, and have 

 two-jointed tarsi, each of which carries at the end either one or two claws. As 

 bird-lice are found on mammals as well as on birds, their name is to some extent 

 misleading. 



TRUE ORTHOPTERA (Orthoptera Genuina). 



The insects of this suborder differ chiefly from those of the last group in the 

 characters of their wings, in which the two pairs are not formed alike. The fore- 

 wings, which are usually stiff and tough, and in some cases horny, serve as wing- 

 covers, and are generally spoken of as elytra ; whereas the hind-pair are 

 membranous, and capable of being folded longitudinally, or both longitudinally 

 and transversely. The division of the ligula, or terminal piece of the lower lip 

 into two or four lobes, is usually more complete than in the Pseudoneuroptera. 

 It is usual to divide the true Orthoptera into two series or tribes the Saltatoria, 

 with strongly-developed hind-legs, adapted for leaping, and the Cursoria, in which 

 the hind-legs are not thus developed, but are better fitted for use in running and 

 walking. The saltatoria, or jumpers, are sometimes spoken of as the Musical 

 Orthoptera, since nearly all these insects, such as crickets, grasshoppers and locusts, 

 are noted for the loud chirping sounds which the males produce. The females are 

 supposed to be attracted by the chirping of the males; they seldom emit any 

 sound themselves, and when they do it is generally of a very feeble character. 

 It is probable that most insects can hear, but by what means they do so is, in the 

 majority of cases, to a great extent a matter of conjecture. The Saltatorial 

 Orthoptera are, however, remarkable in possessing very definite organs of hearing, 

 which, though occupying a different position, are functionally comparable to the 

 ears of higher animals. 



The crickets (Gryllidce) which form the first family of the sub- 

 order, have a somewhat rounded head, supporting long whip-like 

 antennae. Their mandibles are strong and toothed ; the inner lobe of the maxillae 



