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 resembles. The tail, and the upper part of the body, have a singular power of being drawn out, or drawn in, like the tube of a telescope. There is sometimes a shell, or carapace, but often the body is covered only with a smooth firm skin, which, however, presents decided indications of being segmented.

The first person who described these Rotifers was the excellent old Leuwenhoek; and his animals were got from the gutter of a house-top. Since then, they have been minutely studied, and have been shown to be, not Infusoria, as Ehrenberg imagined, but Crustacea. Your attention is requested to the one point which has most contributed to the celebrity of these creatures—their power of resuscitation. Leuwenhoek described—what you have just witnessed, namely—the slow resuscitation of the animal (which seemed as dry as dust, and might have been blown about like any particle of dust,) directly a little moisture was brought to it. Spallanzani startled the world with the announcement that this process of drying and moistening—of killing and reviving—could be repeated fifteen times in succession; so that the Rotifer, whose natural term of life is about eighteen days, might, it was said, be dried and kept for years, and at any time revived by moisture. That which seems now no better than a grain of dust will suddenly awaken to the energetic life of a complex organism, and may again be made as dust by evaporation of the water.

This is very marvellous: so marvellous that a mind, trained in the cultivated caution of science, will demand the evidence on which it is based. Two months ago I should have dismissed the doubt with the assurance that the evidence was ample and rigorous, and the fact indisputable. For not only had the fact been confirmed by the united experience of several investigators: it had stood the test of very severe experiment. Thus in 1842, M. Doyère published experiments which seemed to place it beyond scepticism. Under the air-pump he set some moss, together with vessels containing sulphuric acid, which would absorb every trace of moisture. After leaving the moss thus for a week, he removed it into an oven, the temperature of which was raised to 300° Fahrenheit. Yet even this treatment did not prevent the animals from resuscitating when water was added.

In presence of testimony like this, doubt will seem next to impossible. Nevertheless, my own experiments leave me no choice but to doubt. Not having witnessed M. Doyère's experiment, I am not prepared to say wherein its fallacy lies; but that there is a fallacy, seems to me capable of decisive proof. In M. Pouchet's recent work I first read a distinct denial of the pretended resuscitation of the Rotifers; this denial was the more