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 swallowed—and, suddenly, in its place are unfolded two broad membranes, having each a circle of waving cilia. The lifeless oval has become a living animal! You have assisted at a resuscitation, not from death by drowning, but by drying: the animal has been drowned into life! The unfolded membranes, with their cilia, have so much the appearance of wheels that the name of "Wheel-bearer" (Rotifera) or "Wheel Animalcule" has been given to the animal.

The Rotifera (also—and more correctly—called Rotatoria) form an interesting study. Let us glance at their organization:—

Fig. 16.

A, with the wheels drawn in (at c). B, with wheels expanded; b, eye spots; c, jaws and teeth; f, alimentary canal; g, embryo; h, embryo further developed; i, water-vascular system; k, vent.

There are many different kinds of Rotifers, varying very materially in size and shape; the males, as was stated in the last chapter, being more imperfectly organized than the females. They may be seen either swimming rapidly through the water by means of the vibratile cilia called "wheels," because the optical effect is very much that of a toothed-wheel; or crawling along the side of the glass, fastening to it by the head, and then curving the body till the tail is brought up to the spot, which is then fastened on by the tail, and the head is set free. They may also be seen fastened to a weed, or the glass, by the tail, the body waving to and fro, or thrusting itself straight out, and setting the wheels in active motion. In this attitude the aspect of the jaws is very striking. Leuwenhoek mistook it for the pulsation of a heart, which its incessant rhythm much