Whence come they? said I, in my article. Have they fallen from the sky completely formed? It is evident that they have not been developed on the ground where they have been found; it is not less evident that they appeared suddenly on the borders. Did they come from within the bodies of certain insects which they have quitted, on account of the rain which had fallen? These worms, in fact, had completed their parasitical stage in the bodies of their hosts, and the great drought which had continued for many weeks prevented their resuming their first course of existence. It was the sudden emancipation of so many worms at once which had attracted the attention of gardeners: earwigs, cockchafers, and many other insects give them shelter during the time of this strange gestation. It is known, by the observations of Siebold, that the eggs of the Mermis, laid during the winter, produce in the following spring embryos which live in damp earth. They immediately seek the larvæ of insects, perforate their skin, and develop themselves there without becoming encysted. After this, they again pass through the skin of their host, return to the damp earth, where they change their skin, are fecundated, and lay eggs. The larvæ of _Mermis albicans_ especially resort to caterpillars, or the larvæ of the coleoptera, 180 orthoptera, or diptera, and even to a mollusc, the _Succinea amphibia_. Professor Meissner, and more especially Dr. Grenacher, professor at Göttingen, have made known to us the structure of the Gordius. The _Gordius bifurcus_ produces embryos at the end of a month; these embryos perforate their shell by means of their beak, become free in the damp earth, and introduce themselves through the skin into the perigastric cavity of certain larvæ. The sexual worm again becomes free. If we may believe Mons. Villot, who has made recent observations on the Mermis and the Gordius, the latter alone pass through complete metamorphoses; they assume three different forms, and change their habitation three times. Their first abode must be in the water, or in the larva of a dipterous insect, as a free embryo; the second in the larval state, in the intestines of a fish; and the third, like the first, in a sexual state. To judge by some specimens of gordius brought from India, these curious parasites exist not in Europe only; they have been found in different parts of the world, and they lead everywhere the same kind of life. They have been found in Calcutta in the _Hapale_; in the Philippine Islands in a _Mantis_, and the museum of Hamburg possesses some from Venezuela, which came from the body of a _Blatta_.