PARASITES THAT UNDERGO TRANSMIGRATIONS AND METAMORPHOSES. A certain number of parasites establish themselves at first in an animal which serves as a _crèche_, then in a second which serves as a lying-in hospital. This passage from one animal to another is described under the name of transmigration. In general, the entire _crèche_ with its nurslings passes into the lying-in asylum. The _crèche_ is always represented by an animal which feeds on vegetable diet, which is destined for one which is carnivorous: the lying-in asylum is represented by the latter. The mouse is the _crèche_ which will pass with all its clients into the cat which eats it. If we were treating of plants, we should say that in the first host they are developed, and in the second they blossom. The plant, like the animal, is agamous as long as the flower and the sexual organs have not made their appearance. The animal which migrates usually undergoes a complete change in passing from one abode to another; it is agamous in the first instance, that is to say, without sex, swathed and covered with a padded cap like a nursling; in its last stage it is, on the contrary, endued with all its sexual attributes. In the _crèche_ the parasite is on its passage from one station to 184 another, and that which arrives at the lying-in asylum has reached the end of its journey and is at home. We have proposed to give it the name of _Nostosite_, as distinguished from that which only inhabits its host for a time. We may also remark that the same animal may give lodging to these two kinds of parasites. It is thus that the rabbit harbours in its peritoneum passengers which are only at home in the dog; and, independently of these passengers (these strangers may we say?), it lodges in its intestines a sexual tænoid worm. The first is a _Xenosite_, the second a _Nostosite_. The mouse, in the same manner, gives lodging to passengers under the name of _Cysticerci_, which are destined to the cat in order to become _Tæniæ_. We might call the rabbit or the mouse which harbours worms _in transitu_, the stage coach; more especially as from time to time there are some which miss it, and are consequently lost in their peregrinations. This stage-coach is the intermediate host, the _Zwischenwirth_ of German helminthologists, which is always an animal with a vegetable diet; the final host is generally a carnivore: it is by means of the vegetable feeder, the grazing or herbivorous animal, that the stranger parasite introduces itself.