““It is with the [head louse and body louse] that we are chiefly concerned, and they are so closely related that, even now, by an occasional mésalliance resulting from the meetings of young people about the neck band, a body louse may go native and interbreed with a head louse. The crab louse we may neglect. He is probably of distinct generic origin and a creature that merits neither respect nor sympathy; not even terror.””