other cestodes, is free at the commencement and the end of its life at the beginning, in order to penetrate into its host; at the end, to scatter its eggs.

Messrs. Sommer and Landois published, in 1872, an anatomical description of the sexual organs of the Bothriocephalus latus, of such completeness, that it will be long before any one will again take up this subject, which had so much occupied helminthologists ever since the celebrated work of Eschricht. This memoir is illustrated by superb engravings, which represent these organs under every aspect. Dr. Böttcher, of Dorpat, found in the small intestine of a woman, who died of peritonitis, at least a hundred Bothriocephali. They were but slightly developed, though there were some in a sexual state.

The largest tænia, though not the longest, is the Tænia magna, from the Rhinoceros, described by Marie; it is, no doubt, the same to which the name of gigantea was given by Peters. The learned director of the Museum of Berlin gave me a fine specimen of it eighteen years ago. The generic name of Plagiotania has been proposed for this worm.

Almost all birds nourish large and beautiful tæniæ, but they must be studied immediately after the death of their host. They often change their form entirely at the end of a few hours.

Woodcocks and snipes always have their intestines stuffed full of tæniæ and the eggs of these worms. Every bird contains them by thousands. Fortunately we cannot be infested with the tænia of the snipe and the woodcock.

Fig. 61 represents the scolex of the Tania variabilis

of the snipe, 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.

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 fosse of the dog and the horse a worm resembling a leech, with a body completely etiolated, which lives there entirely as a

a few years.

parasite, and whose history has only been known for Chabert discovered the first species of this group in 1787 in the frontal sinus of the horse and the dog. It had been named Tenia 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.

It is to be presumed that this dreadful parasite has been introduced into man by means of the flesh of the goat, and perhaps of the rabbit. Linguatulæ are found in their primary agamous form, in open cavities like the nasal fossæ. Leuckart was the first to show that the linguatulæ, which lived at first encysted in the peritoneum of the rabbit, completed their evolution and became perfect in the nasal fossæ of the dog. The Linguatula serrata (Fig. 65), which lives primarily in the goat, the guinea-pig, the hare, the

rabbit, &c., is found accidentally in man, and perfect in certain mammals. Examples have been given of sick persons being completely cured by the evacuation of worms from the nostrils; these worms were, doubtless, linguatulæ. Fulvius Angelianus and Vincentius Alsarius speak of a young man who had suffered for a long time from head-ache, and

Fig. 65.-Linguatula magnified six times. Four hooks are seen around the mouth in front. c, the anus.

tænioïdes. These parasites may perhaps sometimes lose their way in their peregrinations. Some years ago a lioness died of peritonitis at Schönbrunn, and, after death, the liver, the spleen, and other organs were found to be filled with encysted linguatulæ.

The nematode worms are long and rounded, like the ordinary ascarides of infants, which take up their abode in all the organs of animals of the various classes of the animal kingdom. About a thousand varieties are known,

varying in length from a few millimètres to forty or fifty centimètres.

They are not all parasites, as has been thought, since some are found in the sea, and others in damp earth, in putrid matter, and even on plants and their seeds. The migrations of nematodes are subjects of great interest. Their changes of form are usually not very considerable; but the modifications in their sexual apparatus, whether in the same individual, or in the succeeding generations, are very curious.

When we consider the numerous encysted and agamous nematodes, which are found in the different orders of mammalia, birds, reptiles, batrachians, and fishes, there is little doubt that all these beings are only migratory parasites, which pass together with their hosts into the animal to which they are destined. They are found, like ascarides, in animals of all classes. Some are to be met with in all the organs-the brain, the eye, the muscles, the heart, the lungs, the tracheal artery, the frontal sinus, the digestive tube, the skin, and even in the blood. Sometimes the two sexes live under the same conditions; sometimes the male is dependent on its female, or else one generation is parasitical, and the next is independent. There is a great diversity with respect to development. Some nematodes, like trichinæ, are developed so rapidly, that the embryos are already perfect in the egg before it has quitted its mother. Others, like the ascarides lumbricoides, lay eggs, in which the embryos do not appear till several weeks or many months after they have been laid. Between these two extremes we find all the intermediate degrees.

Diezing, who has done more for systematic helmin