The lowest of all animals are the _protozoa_, yet even here, as it appears to me, we begin to see the dawnings of that intelligence, without which that kind of interest which the life and acts of any creature should possess, in order to make it the subject for a work like this, can hardly be said to exist. The _infusoria_ stand at the very bottom even of the protozoa. Most of them are so small as to be invisible, except through the microscope, and they are not supposed ever to think. Yet a creature belonging to this humble group, having a cup-shaped body, with a grasping arm or tail to it, has been seen to attach itself, with this, to the cup of another individual of the same species, considerably larger than itself, and cling there with a pertinacity very suggestive of a firm intent. Upon this the larger one became, to all appearance, very excited, and, moving about in the water—for these creatures are aquatic—till it came to some weed, fastened with its one limb on a piece of this, and proceeded to jerk itself backwards and forwards, with great suddenness and vigour, and with the evident design, as it seemed, of ridding itself of the intruder. The latter, however, held on like grim death, and this hard-pitched battle, which had all the appearance of being intelligently directed, went on between these two microscopic and simply formed creatures, for quite a long time. At length the smaller of the two was jerked off, upon which it made a second attempt to establish itself as before, but was defeated by the efforts of its more powerful adversary. The witness of this interesting scene tells us it was very difficult to believe that the two lowly organisms engaged in it, though consisting but of a single cell, without a head and with no trace of a nervous system, properly so called, were not sentient beings, conscious of what they were doing, and of why they were doing it.