It (the contraction) invariably happens when the animal is touched or alarmed, and is, consequently, very frequent when the water swarms with many other swimming animalcula. When it takes place the flower-bell generally closes up into a little round ball, which opens out again only when the stalk becomes fully extended. From this we might almost infer that some animalcule, or other morsel of food, had been seized and retained within the cup; moreover, that the contraction of the stalk assisted in securing or disposing of the prey. This, however, is uncertain. The motions of the Vorticella do not seem much affected by the stalk losing hold of its attachment; but the result of such an accident taking place is that the cilia cause the animal to swim through the water, trailing its thread behind it, and the contraction of the latter merely causes it to be drawn up to the head. There are various species of Vorticellæ. That just described is the simplest, consisting merely of a hemispherical ciliated cup, attached to a single thread. It is barely visible to the naked eye. But there is a compound species which I have this year found to be extremely abundant in my aquarium,--whose occupants, both large and small, it excels in singularity and beauty. In structure it is to the simple Vorticella what a many-branched zoophyte is to an _Actinia_. My attention was first drawn to the presence of this creature by observing some pebbles and fronds of green ulva thickly coated with a fine flocculent down. On closer inspection this growth appeared to consist of a multitude of feathery plumes, about one-sixteenth of an inch in height, and individually of so fine and transparent a texture as to be scarcely discernible to the unassisted sight. On touching one with the point of a fine needle it would instantly shrink up into a small but dense mass, like a ball of white cotton--scarcely so large as a fine grain of sand. In a few seconds it would again unfold and spread itself out to its original size. By carefully detaching a specimen with the point of a needle or pen-knife, and transferring it, along with a drop of water upon a slip of glass, to the stage of the microscope, a sight was presented of great wonder and loveliness:-- 'The more I fixed mine eye, Mine eye the more new wonders did espye!'