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 nearest allied to Pediculus. [Illustration: 121. Louse of Domestic Fowl.] The common barn-yard fowl is infested by a louse that we have called Goniocotes Burnettii (Fig. 121), in honor of the late Dr. W. I. Burnett, a young and talented naturalist and physiologist, who paid more attention than any one else in this country to the study of these parasites, and made a large collection of them, now in the museum of the Boston Society of Natural History. It differs from the G. hologaster of Europe, which lives on the same bird, in the short second joint of the antennae, which are also stouter; and in the long head, the clypeus being much longer and more acutely rounded; while the head is less hollowed out at the insertion of the antennae. The abdomen is oval, and one-half as wide as long, with transverse, broad, irregular bands along the edges of the segments. The mandibles are short and straight, two toothed. The body is slightly yellowish, and variously streaked and banded with pitchy black. The duck is infested by a remarkably slender form (Fig. 122, Philopterus squalidus). Figure 123 represents the louse of the cat, and another species (Fig. 124) of the same genus (Trichodes) lives upon the goat. The most degraded genus is Gyropus. Mr. C. Cook has found Gyropus ovalis of Europe abundant on the Guinea pig. A species is also found on the porpoise; an interesting fact, as this is the only insect we know of that lives parasitically on any marine animal. [Illustration: 122. Duck Louse.]