each, and if some of the vessels are filled with brook-water only, the student will come into possession of many beautiful specimens of both animal and vegetable life, the search for the names and histories of which will be even more profitable than the contemplation of their beauty. The first specimen I ever possessed of the beautiful confervoid Hydrodictyon utriculatum was obtained in this way—the water, after depositing a green sediment, gave birth to a rich net-work of vegetation, in which this conferva was conspicuous. Several of the jars which I prize the most are those which have been simply filled at the brook side, and left for the minute germs of animal and vegetable life to develope in their own way, and it is not long before a rich growth takes place, that affords abundant material for observation with the microscope. Feeding is necessary only in the case of carnivorous larva and beetles, and for these small fish is undoubtedly the best; the herbivorous creatures supply themselves. As a general rule the water in the jars should never be changed; it is by leaving things to themselves that the best display is to be obtained, especially if chara and other low forms of vegetation are preserved.
Nitella is almost too delicate for the tank, but an admirable plant for growth in jars in which cabinet specimens of larvæ are kept. I rarely place it in the aquarium, considering it too choice a thing, its delicate structure rendering it barely perceptible amidst the more luxuriant growths with which it gets entwined. Still, it does well there, but cannot be studied unless a bunch is placed in a glass jar for separate culture. It consists
