Page:Experimental researches in chemistry and.djvu/321

306 each side of the head; they seem formed of deep teeth or short radii, perhaps fourteen or fifteen in number; the form of these teeth is not sharp or well defined, but hazy at the edges; the interval between them is perhaps rather more than the width of the teeth; the teeth are not distinctly set on to a nave or axis, but appear sometimes even to melt away or attenuate at the part towards the centre, and sometimes appear as independent portions, i. e. as much separated from the centre part or supposed place of attachment as from the neighbouring teeth.

These parts are never seen as wheels, except in motion; the animal is sometimes seen without them, the parts which produce the appearance being then either retracted and drawn inwards, or disposed in other forms, for the animal is of a very changeable nature. The motion of the wheels is continuous, as if they were spinning constantly in one direction upon their axis; the velocity is such as to carry the teeth rapidly before the eye, but is not enough to confound the impression of one tooth with that of its neighbours, and therefore they may be distinctly seen. Both wheels move usually in the same direction; and when the head of the animal is towards the observer, the direction is generally the same as that of the hands of a clock. Baker states, however, that he has seen them move in opposite directions, and also has seen the motion first discontinued, and then reversed, in the same wheel. The velocity is not always the same, but varies with the efforts of the animal to catch its food. Whatever the mechanism of the parts, the result is, that currents are established in the water towards the bead of the animal, which currents pass off outward from the edges of the apparent wheels; and little particles Boating in the water may be seen to pass towards the head, and be suddenly thrown off at the edges of the wheels with considerable force.

So striking are the appearances of these animalcule, that men of much practice in microscopical observation are at this day convinced they do possess wheels, which actually revolve continuously in one direction. The struggle in Mr. Baker's mind between the evidence of his senses and his judgment, illustrates this point in so lively a manner, that I may be excused quoting his account of it:—"As I call these parts wheels, I also term the motion of them a rotation, because it has exactly the