The _collection_ of the fresh diatoms is so closely connected with their _preservation_, that a few notes may be given upon it before we pass on. For this purpose a number of small bottles must be provided, which may be placed in a tin box, with a separate apartment for each, so that all chance of breakage may be done away with. The diatoms are generally of a light brown colour; and where they are observed in the water, the bottle may be so placed, with the mouth closed by the finger, that when the finger is withdrawn the water will rush in, carrying the diatoms also. If they are seen upon plants, stones, or any other substance, they may generally be detached and placed in the bottle. When there is a green covering upon the surface of the water, a great quantity of diatoms is usually found amongst it; as also upon the surface of the mud in those ponds where they abound. In these cases, a broad flat spoon will be found very useful, and one is now made with a covering upon the broader portion of it to protect the enclosed matter from being so readily carried off whilst bringing it to the surface again. Where there is any depth of water, and the spoon will not reach the surface of the mud, the bottle must be united to a long rod, and being then carried through the upper portion with the mouth downwards, no water will be received into it; but on reaching the spot required, the bottle-mouth may be turned up, and thus become filled with what is nearest. From the stomachs of common fish--as the cod, sole, haddock, &c.--many specimens of Diatomaceæ may be obtained, but especially from the crab, oyster, mussel, and other shell-fish. Professor Smith states that from these curious receptacles he has taken some with which he has not elsewhere met. To remove them from any of the small shell-fish, it is necessary to take the fish or stomach from the shell, and immerse it in strong hot acid (nitric is the best) until the animal matter is dissolved, when the residue must be washed and treated as the ordinary Diatomaceæ hereinafter described.