develops itself on the brain of the sheep, and occasions the disease known by the name of "gid." This disease may be produced artificially. The sheep which swallows the eggs of this tænia shows the first symptoms of it towards the seventeenth day. If we kill it at this time, we find on the surface of the brain, either at the base or the summit, or sometimes between the hemispheres and the cerebellum, one or more white vesicles of the size of a pea, and on which no traces of buds are yet to be seen. This vesicle, of a milky-white colour, and filled with liquid, is the scolex. Near these vesicles are to be seen some very irregular yellow furrows, like tubes abandoned by some tubicolar annelid; this is the gallery through which the vesicular worm has proceeded to the place where it has been found. A fortnight later, that is to say, about the thirtysecond day, the cœnurus is as large as a small nut, and one can see with the naked eye some small nebulous corpuscles, separate from each other, of the same form and size; these are the buds or scolices which have risen up, but which, as yet, have neither hooks nor suckers. We give the representation of one of these vesicles, on the internal walls of which Fig. 54.-Conurus of the sheep. 1, the enclosed scolex; 2, Hydatic vesicle, with the scolices in their place within it. young scolices have been developed; this is nearly of the natural size. Fig. 2, a, a, shows these scolices of nearly the natural size. Fig. 1 represents an isolated and magnified scolex; A, shows the segments of the future proglottides; D, the suckers; C, the hooks; H, the vesicle which contains them. Eggs of the same tænia have been given to sheep at Copenhagen and at Giessen, and Messrs. Eschricht and R. Leuckart have obtained the same result as we had at Louvain. On the fifteenth or sixteenth day the first symptoms of "gid" declared themselves. At about the thirty-eighth day the crown of hooks appeared, the suckers were formed, and the whole head of the scolex was sketched out. All these heads can leave or enter the sheath at the will of the animal. It is truly a polycephalous animal when the scolices are expanded. This worm continues to grow for a long time in the cranial cavity, and produces by its presence the gravest results. The sheep necessarily dies at last, unless we remove the parasite by means of the trepan. The cœnurus, at this point of development, swallowed by a dog, undergoes great changes in a few hours. The proscolex, or large vesicle, withers; the different scolices unsheath their cephalic extremity, become free, penetrate into the intestine with the food, and attach themselves to its walls, so as to form as many colonies of tænia as there are distinct heads. A dog which has swallowed a single cœnurus may therefore contain a considerable number of tæniæ. The development of this worm proceeds very rapidly, and it only requires three or four weeks to attain many feet in length. The organization of this worm, in the state of strobila and of proglottis, is in every respect like that of the Tænia serrata; we have even endeavoured in vain to distinguish these worms from each other by their hooks. The wolf or the dog follows the flock of sheep, scatters the proglottides or the eggs in their way, and the sheep, browsing on the grass with the eggs attached, become infested with their most dangerous enemy. To arrest this disease, only one thing is necessary, to destroy by fire the head of every sheep attacked by the gid." The rest of the animal may be eaten without danger. 66 Pouchet did not succeed in giving sheep the "gid" at first, for the very simple reason that he employed the eggs of the Taenia serrata, instead of those of the Tania cœnurus; he had confounded the two species. The cœnurus of the sheep is a true calamity when it spreads in a country. The animal attacked by it is lost, and the mischief may be indefinitely propagated by giving as food to dogs the head of the sick animal, with thousands of young tæniæ enclosed within each. There exists a singular cestode which bears the name of Echinococcus. We give a figure of the echinococcus of the pig, slightly magnified, and an isolated scolex (Figs. 55 and 56). In its first form it is composed of closed sacs, which grow to the size of a nut, and some times to that of an orange. It usually lodges in the liver of the pig, but establishes itself also in man. We have been assured that part of the population of Iceland have been attacked by it. The abundance of this parasite in that country is attributed to the want of cleanliness, and the number of dogs that they keep around them. The echinococcus becomes a tænia in this animal. It scatters the eggs with its dung, leaving them directly or indirectly on plants which the Icelanders eat; for they gather for food certain mosses, sorrel, cochlearia, dandelion, &c., from the midst of the plains in which live flocks of sheep guarded by dogs. The eggs are scattered everywhere on plants or in the water. Leuckart has made some very interesting experiments on the echinococci. In Fig. 57 is shown a tænia which proceeds from an echinococcus. There is yet another tape-worm harboured by man, the Tænia lata, better known under the name of Bothrio |