113. Body Louse.
112. Head Louse.
Under a high power of the microscope specimens treated with diluted potash show that the mandibles and maxillæ arise near each other in the middle of the head opposite the eyes, their bases slightly diverging. Thence they converge to the mouth, over which they meet, and beyond are free, being hollow, thin bands of chitine, meeting like the maxillæ, or tongue, of butterflies to form a hollow tube for suction. The mandibles each suddenly end in a curved, slender filament, which is probably used as a tactile organ to explore the best sites in the flesh of their victim for drawing blood. On the other hand the maxillæ, which are much narrower than the mandibles, become rounded towards the end, bristle like, and tipped with numerous exceedingly fine barbs, by which the bug anchors itself in the flesh, while the blood is pumped through the mandibles. The base of the large, tubular labium, or beak, which ensheathes the mandibles and maxillæ, is opposite the end of the clypeus or front edge of the upper side of the head, and at a distance beyond the mouth equal to the breadth of the labium itself. The labium, which is divided into three joints, becomes flattened towards the tip, which is square, and ends in two thin membranous lobes, probably endowed with a slight sense of touch. On comparing these parts with those of the louse, it will be seen how much alike they are with the exception of the labium, a very variable organ in the Hemiptera. From the long sucker of the Pediculus, to the stout chitinous jaws of the Mallophaga, or bird lice, is a sudden transition, but on comparing the rest of the head and body it will be seen that the distinction only amounts to a family one, though Burmeister placed the Mallophaga among the Orthoptera (grasshoppers and crickets) on account of the mandibles being adapted for biting. It has been a common source of error to depend too much upon one or a single set of organs. Insects have been classified on characters drawn from the wings, or the number of the joints of the tarsi, or the form of the mouth parts. We must take into account in endeavoring to ascertain the limits of natural groups, as the internal anatomy and the embryology and metamorphosis of insects, before we can hope to obtain a natural classification.
The family of bird lice is a very extensive one, embracing many genera, and several hundred species. One or more species infest the skin of all our domestic and wild mammals and birds, some birds sheltering beneath their feathers four or five species of lice. Before giving a hasty account of some of our more common species; we will give a sketch of the embryological history of the lice, with special reference to the structure of the mouth parts.
114. Embryo of the Louse.
115. Mouth Parts of the Louse.
The eggs (Fig. 114, egg of the head louse) are long, oval, somewhat pear-shaped, with the hinder end somewhat pointed, while the anterior end is flattened, and bears little conical micropyles (m, minute orifices for the passage of the spermatozoa into the egg), which vary in form in the different species and genera; the opposite end of the egg is provided with a few bristles. The female attaches her eggs to the hairs or feathers of her host.