Fig. 62.—Tænia variabilis from the snipe. (Crown of hooks.)
Fig. 63.—Tetrarhynchus appendiculatus from the plaice.
There are other worms which migrate, and even some articulate animals; but their modifications of form are much fewer than in the preceding, and their changes are generally restricted to simple metamorphoses. We will place at the head of this chapter the Linguatulæ, which have so perplexed naturalists.
We sometimes find in the nasal fossæ of the dog and the horse a worm resembling a leech, with a body completely etiolated, which lives there entirely as a
parasite, and whose history has only been known for a few years. Chabert discovered the first species of this group in 1787 in the frontal sinus of the horse and the dog. It had been named Tænia lanceolata. All naturalists, Cuvier included, placed this animal among intestinal worms, under the name of Linguatula or Pentastoma. The latter name had been given to it, because they mistook the hooks for mouths.
We have shown, from the embryos, in 1848, that the Linguatulæ, instead of being worms, are articulate animals, more allied to the lerneans or acaridæ than to the helmintha. These observations, though received at first with much hesitation, were fully confirmed afterwards, especially by the learned researches of Leuckart. The linguatulæ have a very long body, sometimes rounded, in other cases compressed, with a mouth surrounded by four strong hooks, regularly disposed in a semicircle. They have often been found in the lungs of serpents, in certain birds, and in many mammals. A linguatula was also seen by Bilharz at Cairo, in the liver of a negro, and they have been observed in the hospitals of Dresden and Vienna.