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I] sometimes presenting one or more swellings in their continuity, the microgametes are three or four times as long as a blood corpuscle is broad. At first they are attached to the periphery of the pigmented central, more or less spherical body, which is about half the diameter of a red blood-corpuscle. Their movements are so vigorous that they double up or otherwise distort temporarily those corpuscles with which they chance to come in contact. Occasionally it may be observed that one or more of the microgametes

Fig. 4. Malaria parasite: flagellated body and free-swimming microgamete.

break away from the central sphere and swim free in the blood (Fig. 4), remaining active for a considerable time—several hours, perhaps—before finally vanishing. When swimming free in the plasma, and also while still attached to the sphere, the microgamete indulges in three kinds of movement: (a) an undulatory movement, evidently subserving locomotion; (b) a vibratory movement, apparently provoked by contact with a resisting body, as a blood corpuscle, for in such circumstances the little filament is sometimes seen to straighten itself out and quiver like a slender rod when it is struck on the ground; (c) a B*