Coming now to the invertebrates, much has been written concerning the psychology and intelligence of ants and bees. What shall we say concerning their constructs? For reasons already given, I think we may suppose that they are analogous to ours; but it can scarcely be that they in any way closely resemble ours. Their sense-organs are constructed on a different plan from ours; they have probably senses of which we are wholly ignorant. Is it conceivable, by any one who has grasped the principle of construction, that with these differently organized senses and these other senses than ours, the world they construct can much resemble the world we construct? Remember how largely our perceptual world is the product of our geometrical senses—of our delicate and accurate sense of touch, and of our binocular vision, with its delicate and accurate muscular adjustments. Remember how largely these muscular adjustments enter into our perceptual world as constructed in vision. And then remember, on the other hand, that the bee is encased in a hard skin (the chitinous exoskeleton), and that its tactile sensations are mainly excited by means of touch-hairs seated thereon. Remember its compound eye with mosaic vision, coarser by far than our retinal vision, and its ocelli of problematical value, and the complete absence of muscular adjustment in either the one or the other. Can we conceive that, with organs so different, anything like a similar perceptual world can be elaborated in the insect mind? I for one cannot. Admitting, therefore, that their perceptions may be fairly surmised to be analogous, that their world is the result of construction, I do not see how we can for one moment suppose that the perceptual world they construct can in any accurate sense be said to resemble ours. For all that, the processes of discrimination, localization, outward projection; the formation of vague constructs, their definition through experience, and the association of reconstructs or representations;—all these processes are presumably similar in kind to those of which we have evidence in ourselves.
In considering such organisms as ants and bees, however, we must be careful to avoid the error of supposing that, because they happen to have no backbones, they are necessarily low in the scale of life and intelligence. The tree of life has many branches, and, according to the theory of evolution, these divergent branches have been growing up side by side. There is no reason whatever why the bee and the ant, in their branch of life, should not have attained as high a development of structure and intelligence as the elephant or the dog in their branch of life. I do not say that they have. As it is difficult to compare their structure, in complexity and efficiency, with that of vertebrates, so is it difficult to compare their intelligence. The mere matter of size may have necessitated the condensation of intelligence into instinct in a far higher degree than was required in the big-brained mammals. Still, their intelligence, though of a different order and on a different plane, may well be as high. And Darwin has said that the so-called brain of the ant may perhaps be regarded as the most wonderful piece of matter in the world.
That ants have some power of communication seems to be proved by the interesting experiments of Sir John Lubbock. He found that they could carry information to the nest of the presence of larvæ, and that the greater the number of larvæ to be fetched, the greater the number of ants brought out to fetch them in a given time. On one occasion Sir John Lubbock put an ant to some larvæ. "She examined them carefully, and went home without taking one. At this time no other ants were out of the nest. In less than a minute she came out again with eight friends, and the little group made straight for the heap of larvæ. When they had gone two-thirds of the way, I imprisoned the marked ant; the others hesitated a few minutes, and then, with curious quickness, returned home." This is only one observation out of many; and it shows (1) that since the marked ant took no larva home, she must have given information which led the others to come out—unless we can suppose that the smell of the larvæ she had examined still hung about her; and (2) that the communication was not detailed, and probably was no more than "Come," for, when the leader of the party was removed, the rest knew not[GR] where to go—very possibly knew not why they had been summoned.
Passing now to creatures of lower organization, it is exceedingly difficult so to divest ourselves of our own special mental garments as to imagine what their simple and rudimentary constructs are like. Perhaps we may fairly surmise that, as visual, olfactory and auditory organs develop, and differentiate from a common basis of more simple sensation, the process of outward projection has its rudimentary inception. The earthworm, which finds its way to favourite food-stuffs buried in the earth in which it lives, would seem to possess the power of outward projection in a dim and possibly not very definite form. Through their marginal bodies—simple auditory or visual organs—the medusæ may have a rudimentary form of this capacity. In any case, they seem to have the power of localization. Mr. Romanes says,[GS] "A medusa being an umbrella-shaped animal, in which the whole of the surface of the handle and the whole of the concave surface of the umbrella is sensitive to all kinds of stimulation, if any point in the last-named surface is gently touched with a camel-hair brush or other soft (or hard) object, the handle or manubrium is (in the case of many species) immediately moved over to that point, in order to examine or brush away the foreign body." And the same author thus describes[GT] the process of discrimination in the sea-anemone: "I have observed that if a sea-anemone is placed in an aquarium tank, and allowed to fasten upon one side of the tank near the surface of the water, and if a jet of sea-water is made to play continuously and forcibly upon the anemone from above, the result, of course, is that the animal becomes surrounded by a turmoil of water and air-bubbles. Yet, after a short time, it becomes so accustomed to this turmoil that it will expand its tentacles in search of food, just as it does when placed in calm water. If now one of the expanded tentacles is gently touched with a solid body, all the others close around that body in just the same way as they would were they expanded in calm water. That is to say, the tentacles are able to discriminate between the stimulus which is supplied by the turmoil of the water, and that which is supplied by their contact with the solid body, and they respond to the latter stimulus notwithstanding that it is of incomparably less intensity than the former."
Here, in discrimination, we reach the lowest stage of mental activity. It is exceedingly difficult, however, to determine how far such simple responses to stimuli are merely organic, and how far there enters a psychological element.
I ought not, perhaps, to pass over in perfect silence the subject of protozoan psychology. M. Binet has published a little book on "The Psychic Life of Micro-Organisms," in the preface of which he says, "We could, if it were necessary, take every single one of the psychical faculties which M. Romanes reserves for animals more or less advanced on the zoological scale, and show that the greater part of these faculties belonged equally to micro-organisms." He says that "there is not a single infusory that cannot be frightened, and that does not manifest its fear by a rapid flight through the liquid of the preparation," and he speaks of infusoria fleeing "in all directions like a flock of frightened sheep." He attributes memory to Folliculina, and instinct "of great precision" to Difflugia. He regards some of these animalculæ as "endowed with memory and volition," and he describes the following stages:—
"1. The perception of the external object.
"2. The choice made between a number of objects.
"3. The perception of their position in space.