expense, but which has been hitherto found only in Egypt.
We know perfectly well the itinerary of the Tænia serrata of the dog, which is so abundant, that there are few of these animals that do not enclose some and even many of them. There are few except lapdogs which do not harbour them. We can easily assign the reason. Every tænia, like every animal, has its eggs; each plant has its seeds. These eggs are laid by the mother in the most favourable condition for the development of her progeny. The dog deposits its dung on the grass rather than in any other spot, because the eggs of its tænia, which are destined to the rabbits or hares, will have greater chance of arriving at their destination than if they were exposed on the bare earth, or in the water. Their prodigious number is calculated according to the chances of their arriving safely. The egg, when introduced into the stomach of the rabbit, is rapidly hatched in this organ under the action of the gastric juice, and the embryo which is produced from it seeks its hiding-place in the midst of the tissues which surround it; it bores into them, and establishes itself in the folds of the peritoneum. Then, once in its resting-place, it barricades itself, and waits patiently for an opportunity of introducing itself into the stomach of the dog.
This microscopic embryo is armed with six hooks, like embryos of all the cestodes; it employs them with much dexterity to pierce the walls of the organs, and to hollow out a space for itself in the substance of the tissues. Shut up in its hiding-place, membranes form around for its protection; its six hooks, having become useless, wither;
other hooks in the form of a crown appear by the side of four rounded projections, the future suckers; and, sheathed in a large vesicle full of a limpid fluid, it waits patiently for the moment when it will find a place in the stomach of a dog. If good fortune awaits it, it will wake up, some fine day, in the stomach of the animal which has eaten the rabbit, its former home, and a new life will commence for it. The organs in which it was imprisoned are digested, it gets rid of all its swaddling-clothes, unrolls itself, separates from the vesicle which has protected it hitherto, and penetrates into the intestine; there, immersed in the food of its host, it grows with extreme rapidity, and assumes the form of a ribbon or tape. The ends of this tape are successively matured, detach themselves, and become the complete worms, full of eggs, which are evacuated with the feces; scarcely have they made their appearance in the open air before they burst and scatter their eggs.
He whose scientific curiosity is sharpened, has only to watch the dung of the dog at the moment of its evacuation to distinguish on its surface worms of a milky-white colour, contracting like leeches, which are the true Tænia serrata in its adult state. Experiments made on this species have given sanction to what I had said respecting the cestodes.
The tænia, under the name of Cysticercus cellulosus, lives in the folds of the peritoneum of the rabbit and the hare, and passes directly from the rabbit to the dog to become complete.
It is very curious that the fox, so nearly allied to the dog in appearance, and which also eats rabbits, never has the Tænia serrata, but this animal nourishes other worms.
It was with these cysticerci that I made experiments on four dogs, which I took with me to Paris, in order to convince those who could not believe in the migration of parasites. It was this species that I gave also to the dogs which served as a demonstration at Paris at the course of lectures given by Mons. Lacaze Duthiers.
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 Cœnurus 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 Cœnurus cerebralis; this