_Crustacees._--These animals are almost all aquatic and the greatest part in the seas. Crabs are found generally near the shore in the hollows of the rocks and under the stones; but there are kinds which hide in the sand or which live at great depths; some live entirely in the sea. It is the same for the decapodes macroures, such as the langoustes and the salicoes; and it is generally by the aid of drags and nets that they are taken; but a more successful way of fishing is to sink to the bottom an open case, a kind of basket whose mouth is in the form of a reversed cone; some carrion placed in the interior of this snare attracts the crabs, and when once in they cannot get out. The small kinds of crevettines are found, in great abundance, in the midst of the sea-weed; and to catch them, it is necessary to place a certain quantity of marine plants in a vase full of sea-water: the little animals that are in it quickly exhaust the oxygen dissolved in this liquid and they rise to the surface where it is easy to take them with a spoon. Other crustacees of small size are found in the deep sea and are taken in nets like the sea mollusques. Besides, there exist a great number of these animals, who live as parasits on fish (about the gills especially), and by a collection of them science would be enriched by a multitude of new and curious specific form. Until now travellers have almost entirely neglected the little crustacees of the order of the entomostracees, which are found in fresh water; and it is desirable that they should be collected in all localities. The best means of preservation of the crustaces is to plunge them in alcohol from 20 to 25 deg., after having wrapped them in linen or leaves. The large kinds shall be dried, by taking care first to take out the viscera that are under the shell; but the crustacees preserved in this manner are extremely fragile and it is rare to preserve them entire. _Fish and reptiles._--Although among sea fish there are several kinds which are found in different coasts, the greatest number inhabit particular shores and gulfs. It would be useful then to send those that are found in countries not yet visited by naturalists and even the common market fish. As for the fresh-water fish, they differ, not only according to the country, but according to the rivers and lakes where they live. It would be well to send all that can be found. Generally, any fish brought from a foreign market, with the name that it bears in the country, would be an acquisition interesting for science. They should be put in alcohol, or, if too large, only the skin well dried, taking care to preserve the head, teeth and fins. It is essential that the fins should be stretched out in order to dry them well. For this they should be glued on paper.