Fig. 61 represents the scolex of the _Tænia variabilis_ of the snipe, 230 and Fig. 62, by its side, shows the crown of hooks more highly magnified. We have made these drawings from worms collected from snipes some instants after their death. We close this chapter on the cestodes with the plate (Fig. 63) of a Tetrarhynchus which is usually found in the plaice. The perfect tetrarhynchi, that is to say, those that are adult and sexual, inhabit the intestines of voracious fishes, especially of the squalidæ. [Illustration: Fig. 61.--Tænia variabilis from the snipe.] [Illustration: Fig. 62.--Tænia variabilis from the snipe. (Crown of hooks.)] [Illustration: 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 231 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.