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or conjugation may often be observed: and I once met with a whole colony, produced by progressive self-division, all thrusting out their heads from the muddle of a limp of jelly, which served as their common envelope.

The bell-shaped Vorticelllæ are familiar to every microscopist, and they are as beautiful as they are common. They are often so abundant as to look like a white fluff clothing the roots and stems of aquatic plants. The bell has no cilia on its surface; but from the open rim protrudes a disk which beats a rotary wreath of these organs. In the depression between rim and disk lie the month and the excretory orifice close together. The former opens into a well-defined gullet, which extends some way into the interior, where also a contractile vesicle and a curved nucleus may readily be discerned. Careful illumination is needed to show the contractile thread inside the tubular stalk. When a Vorticela breaks away from its place of attachment, as not infrequently happens, the bell may swim of with the stalk in tow. In one such instance I observed the bell come to rest by its cilia on a bit of weed; and while in that position, the stalk every now and then contracted spirally as usual, although the movement could be of no possible use to the creature. This led me to think that the movements is ordinarily quite independent of anything of the nature of will. Specimens may be met with in various stages of fission; and occasionally one or two small oval bodies are found adhering to the stalk where it joins the bell, but what part they play in the life-history of Vorticella I have not been able to witness.

Continuous self-division increases the number of individuals by a sort of geometrical progression. In such a way are probably formed those splendid compound clusters which, as in Carchesium polypinum, exhibit the magnificent spectacle of forty or fifty bells connected by their ramifying threads with one common trunk. It is a fine sight to behold a number of bunches all contract their fibres at the same moment to one centre, the top of their common pedicel, and to spread out again in loose array as before; and to see this done again and again, not by one specimen alone, but by a colony of specimens crowding the bit of water-plant under examination. I have taken Carchesium on Ancharis from under the ice in the month of January.

Minute Vorticelline forms are found in parasitic clusters on the carapaces of Cyclops, Daphnia, and other Entomostraca; on the shells of water-snails, on water-beetles, and on various aquatic larvæ. Not that the so-called parasites actually feed upon the substance of their host; they do not claim board, but only lodging. They feed in the surrounding element, as usual, by their cilia. Epistylis digitalis infests in thick masses the abdomen of Cyclops, having the appearance of an elegant but rather cumbersome train. The bell-part is ⁠1/430⁠ of an inch long; the little stalk is branched and non-contractile, A much smaller species, with a simple stalk, is a length of no more than ⁠1/2625⁠ of an inch, I have also met with a sessile form, filled with grains of chlorophyll, and completely colouring the abdomen of the unfortunate Cyclops green. Length of body from ⁠1/913⁠ to ⁠1/1028⁠ of an inch.