We may take from the writings[1] of Dr. H. S. Jennings, of Harvard, some account of other modes of behaviour among Paramecia. They largely feed upon clotted masses of bacteria. If a number are placed upon a glass slip, together with a small bacterial clot, they will be seen to congregate around the clot and to feed upon it. All apparently press in so as to reach it, or get as near it as possible. And if a number be placed on another slide without any clot, they soon collect in groups in one or more regions, as in Fig. 2, III. It appears as if they were actuated by some social impulse leading them to crowd together and shun isolated positions. Nay, more; it seems as if, after thus collecting and crowding in to some centre of interest, the attractive influence gradually waned; the group spreads, and the Paramecia are less densely packed; the assembly scatters more and more, but still seems to be retained by an invisible boundary beyond which the little creatures do not pass.
[Illustration: FIG. 2.--Behaviour of Paramecia (after Jennings).]
Furthermore, if kept in a jar, the Paramecia crowd up towards the surface where the bacteria clots are floating; and if, beneath the cover glass of a slip on which they are under microscopic examination, a drop of liquid be introduced through a very fine tube, they will seem either to be attracted to it, as in Fig. 2, I., or repelled from it, as in Fig. 2, II., according to its nature. From alkaline liquids they are repelled; to slightly acid drops they are attracted, unless the acidity be too pungent. Heat and cold are alike repellent, and even a drop of pure distilled water forms an area into which the Paramecia do not enter.
With such facts before him, the incautious observer may be led to the conclusion that Paramecia are not only conscious, but endowed with intelligence and volition. Even M. Binet,[2] who occupies a position which should lead him to exercise more caution, tells us that there is not a single infusorian which cannot be frightened, and does not manifest its fear by rapid flight; he speaks of some of these unicellular animals as “endowed with memory and volition,” and possessed of “instinct of great precision;” and he describes the following stages:--