Some years ago, while making a post-mortem examination, at the Museum of Paris, of some young dogs which I had previously infected with _Tænia serrata_ at Louvain, there were found by the side of these some _Tæniæ cucumerinæ_. These dogs had taken nothing but milk and cysticerci! Whence came these _Tæniæ cucumerinæ_? I knew not, and I frankly owned it to the members of the Commission who proposed the question to me. This however did not prevent my being greatly puzzled with the presence of this worm of whose origin I had no idea. Now we know whence they came. An acaris, the Trichodectes, lives in the hair of young dogs and harbours the scolex of this cestode. The dog, by licking its own hair, grows infested, like the horse, which in a similar manner introduces the gad-fly, and although it has taken no other nourishment, harbours its own epizoaria. The name of _Cysticercus tenuicollis_ has been given to a vesicular worm which inhabits the peritoneum of the ox, the goat, the sheep, &c., and which turns to a tænia in the digestive tube of the dog. Mons. Baillet has made the principal experiments on this transmigration. The itinerary of another cestode worm, the _Coenurus_ of the sheep, is to pass through the sheep in order to reach the wolf or the dog. This worm has only lately been recognized in its tænoïd form; it has, on the contrary, been long known under the name of _Coenurus cerebralis_; this develops itself on the brain of the 223 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. [Illustration: Fig. 54.--Coenurus of the sheep. 1, the enclosed scolex; 2, Hydatic vesicle, with the scolices in their place within it.] A fortnight later, that is to say, about the thirty-second day, the coenurus 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.