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INSECTS. 
Bird-Lice. 
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 
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 
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 Genuinci). 
Psocus lineatus (enlarged three times). 
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- 
Crickets. _ _ 
order, have a somewhat rounded head, supporting long whip-like 
antennae. Their mandibles are strong and toothed; the inner lobe of the maxillae 
