The motion of the animalcules is seldom performed by the vesicular feet. The Frustuliae and Naviculae swim by a slow motion of the whole body; the Cosmaria and Euastra, by floating; the Diatomeae, by moving every one of their limbs; and the Oscillatoriae by a vermicular creeping, similar to the motion of earth-worms. Ophiothrix derives its name from the serpentine and spiral motion, and from the quickness of this animalcule, comparatively superior to that of all the creatures of this series.
The Sphaerodesmi (fig. 85—87.) roll themselves by a floating motion, and rise by a spiral one, by means of which, though slowly, these animalcules ascend from the bottom to the surface of the water, and go down again.
The act of creeping, peculiar to several Oscillatoriae seems to be performed by pressure upon neighbouring filaments or other parts. Some of these animalcules are always seen creeping in company under the microscope.
The Oscillatoria subulata (fig. 71—72), standing upright, cannot creep with the whole body, but that remarkable creature seems to be constantly employed to its own propagation, considering that the coat of the mother opens itself again, as well as the still younger one (c. d. e.). This last filament in the place where it abandons the opening of the coat, is articulated, as well as the coloured content of the maternal filament (d.). These articular nodes are separated by filiform intervals and represent a rosary,
