der side of
the head, of which the foremost and longest are the antennae (_as_),
those succeeding are the mandibles, maxillae, and second maxillae, or
labium. Behind them arise six long, slender tubercles forming the legs,
and the primitive streak rudely marks the lower wall of the thorax and
abdomen not yet formed. Figure 115 represents the head and mouth parts
of the embryo of the same louse; _vk_ is the forehead, or clypeus;
_ant_, the antennae; _mad_, the mandibles; _max_1, the
first pair of maxillae, and _max_^2, the second pair
of maxillae, or labium. Figure 116 represents the mouth parts of the
same insect a little farther advanced, with the jaws and labium
elongated and closely folded together. Figure 117 represents the same
still farther advanced; the mandibles (_mad_) are sharp, and resemble
the jaws of the Mallophaga; and the maxillae (_max_^1) and labium
(_max_^2) are still large, while afterwards the labium becomes nearly
obsolete. Figure 118 represents a front view of the mouth parts of a
bird louse, Goniodes; _lb_, is the upper lip, or labrum, lying under the
clypeus; _mad_, the mandibles; max, the maxillae; _l_, the lyre-formed
piece; and _pl_, the "plate."

[Illustration: 119. Louse of Cow.]

We will now describe some of the common species of lice found on a few
of our domestic animals, and the mallophagous parasites occurring on
certain mammals and birds. The family Pediculina, or true lice, is
higher than the bird lice, their mouth parts, as well as the structure
of the head, resembling the true Hemiptera, especially the bed bug. The
clypeus, or front of the head, is much smaller than in the bird lice,
the latter retaining the enlarged forehead of the embryo, it being in
some species half as large as the rest of the head.

All of our domestic mammals and birds are plagued by one or more species
of lice. Figure 119 represents the Haematopinus vituli, which is brownish
in color. As the specimen figured came from the Burnett collection of
the Boston Society of Natural History, together with those of the goat
louse, the louse of the common fowl, and of the cat, they are
undoubtedly naturalized here. Quite a different species is the louse of
the hog (H. suis, Fig. 120).

[Illustration: 120. Louse of Hog.]

The remaining parasites belong to the skin-biting lice, or Mallophaga,
and I will speak of the several genera referred to in their natural
order, beginning with the highest form and that which is n