A very curious circumstance is the actual rarity of the Bothriocephalus among the inhabitants of the shores of the Lake of Geneva, though formerly it was very common there. This diminution, if we may not call it disappearance, is due to the change which has been made in the construction of water-closets, all of which formerly emptied themselves into the lake, so that the embryos were hatched in the water, and persons were infested by them through drinking it. At present the refuse of the towns is carefully collected for the purpose of manuring the land. This is the result of the advice of Mons. de Candolle, half a century ago; for this naturalist clearly understood how great was the loss to agriculture from the neglect of this fertilizing agent. The itinerary of this tape-worm is simple. It passes from man to the water under the form of an egg, or of a proglottis; and from the water to man in the shape of a ciliated embryo. In this manner it is introduced with the water that is drunk. The Bothriocephalus, like other cestodes, is free at the commencement and the end of its life: 229 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 _Plagiotænia_ 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.