The Medina, or Guinea worm (_Filaria Medinensis, dracunculus_) (Fig. 32), is the terror of travellers who visit the coast of Guinea; it is common, not only on the western coast of Africa, but also in many other parts of this vast continent, and has been recently found in Turkistan and South Carolina (Mitchell). It was formerly thought that this Filaria could introduce itself directly through the skin as a microscopic embryo; but Mons. Fedschenko, after some observations made on the spot, and corroborated experimentally afterwards by Leuckart, is of opinion that this worm is transmitted by means of the Cyclops, a little fresh-water crustacean. Thus the parasite is received by means of the water which is drunk; and this remark is 153 the more important since it will henceforth be only necessary to make use of carefully filtered water in order to guard against it. At the end of six weeks, the presence of the animal is revealed by tumours, the true nature of which is not ascertained at first; then some wounds appear, caused not directly by the worm, but indirectly in consequence of the dissemination of its eggs. The Filaria at last is so entirely atrophied that Professor Jacobson, after having seen it alive on one of his patients at Copenhagen, wrote to Blainville: "This Medina worm is not really a worm, it is a sheath full of eggs." In fact, all the internal organs disappear and nothing exists there except the eggs and their embryos. [Illustration: Fig. 32.--Young Filaria of Medina; 1, Anterior extremity; _c._ Mouth; 2, Caudal extremity; _d._ Anus; 3, Section of the Body.] The Filaria is not allied to the _Mermis_, as was formerly thought; its organization is different, and its organs become atrophied in a very different manner. The _Gordius ornatus_, brought from the Philippines by Professor Semper, has given us an opportunity, by different anatomical observations, to correct many errors, especially with respect to the digestive apparatus (Grenacher). The _Filaria immitis_ is a species found by Mons. Krabbe in a dog which died of 154 a disease to which these animals are subject; it lived in the heart, and twelve individuals, ten females and two males, were found to be lodged there. Mons. Bap. Molin has published a monograph on the Filariæ, giving the characters of 152 species met with in molluscs, fishes, amphibians, reptiles, birds, and mammals: it seems evident that many species have been confounded under the same name.