A table of the birds and mammals on which Mallophaga have been found, together with the names of the latter, has been given by Giebel.[274] The classification of the group, so far as the principal divisions are concerned, by no means accords with the kind of animals that serve as hosts, for the only two genera peculiar to quadrupeds (_Trichodectes_, Fig. 220; and _Gyropus_) belong to the two chief divisions of Mallophaga. The genus _Menopon_ includes numerous species found on birds, and three or four others peculiar to mammals. Two very natural divisions, Philopterides and Liotheides, were adopted by Giebel and Nitzsch, but unfortunately the chief character they made use of for diagnosing the two groups—the presence or absence of maxillary palpi—was illusory. Apparently the labial palps will serve the purpose of distinguishing the two divisions, they being present in the Liotheides and absent in the Philopterides. A table of the characters of the avicolous genera of these two groups is given by Grosse.[275] The Liotheides are more active Insects, and leave their host after its death to seek another. But the Philopterides do not do so, and die in about three days after the death of their host. Possibly Mallophaga may be transferred from one bird to another {351}by means of the parasitic two-winged flies that infest birds. The writer has recorded[276] a case in which a specimen of one of these bird-flies captured on the wing was found to have some Mallophaga attached to it. We should perhaps point out that these Mallophaga, though called bird-lice, have nothing to do with the true lice which are so frequently found with them, and that live by sucking the blood of their hosts. It would in fact be better to drop the name of bird-lice altogether, and call the Mallophaga biting lice. _Trichodectes latus_, according to this method, would be known as the biting louse of the dog, the true or sucking louse of which animal is _Haematopinus piliferus_, and belongs to the anoplurous division of Hemiptera. FAM. II. EMBIIDAE. _Elongate feeble Insects; with small prothorax, elongate meso- and meta-thorax, which may either bear wing or be without them. In the former case these organs are not caducous, are delicately membranous, and all of one consistence, with three or four indefinite longitudinal nervures and a few cross-veinlets. The development is incompletely known. The individuals do not form organised societies._ [Illustration: FIG. 222.—_Oligotoma michaeli._ (After M‘Lachlan.)] The Embiidae are one of the smallest families of Insects; not more than twenty species are known from all parts of the world, and it is probable that only a few hundred actually exist. They are small and feeble Insects of unattractive appearance, and shrivel so much after death as to render it difficult to ascertain their characters. They require a warm climate. Hence {352}it is not a matter for surprise that little should be known about them.