§ 6. Learning by Experience. — In contrast to the sensation-reflex, perceptual activity profits by the results of past experience. It can do so without any distinct revival of the special items of sensation, as they originally occurred. The unity and continuity of impulse which binds a sequence of distinct acts into a single action has its counterpart on the side of retentiveness in the formation of a cumulative disposition. On the first occurrence of the process the traces left by prior phases persist in and contribute to determine succeeding phases. They unite in a single cumulative disposition. When the activity is repeated, whatever stimulus prompts, it reexcites the total cumulative disposition left behind by its previous occurrence. The cumulative disposition has been modified in the anterior experience, and accordingly the rearoused activity takes a correspondingly modified course. This is the process which we have described as acquirement of meaning* Without this there can be no learning by experience of an intelligent kind; and intelligent learning by experience may be due to it alone. Where further processes of reproduction are present, they cooperate with the acquirement of meaning, and make it more definite; but the acquirement of meaning is the primary and indispensable condition of the variation of future activity, in intelligent correspondence with the results of past activity. We shall have hereafter to discuss at what point learning by experience leaves the merely perceptual level and involves ideas. We now give instances of typically perceptual cases. Let us refer once more to Mr. Lloyd Morgan's chickens. "A young chick two days old .... had learnt to pick out pieces of yolk from others of white of egg. I cut little bits of orangepeel of about the same size as the pieces of yolk, and one of these was soon seized, but at once relinquished, the chick shaking his head. Seizing another, he held it for a moment in the bill, but then dropped it and scratched at the base of his beak. That was enough; he could not again be induced to seize a piece of orangepeel. The obnoxious material was now removed, and pieces of yolk of egg substituted, but they were left untouched, being probably taken for orangepeel. Subsequently, he looked at the yolk with hesitation, but presently pecked doubtfully, not seizing, but merely touching. Then he pecked again, seized, and swallowed."+ This illustration well brings out the intelligent nature of the learning by experience. The chicken looks hesitatingly at the yolk; he then makes a tentative peck, only touching it to try what it is like before venturing to seize it. When this preliminary trial proves satisfactory, he pecks again, seizes, and swallows. Take another illustration from a widely different part of the animal creation. Cephalopods, such as the octopus, grope about in all directions with their arms on the ground and on rocks for small mussels and prawns, or they push their armlike tentacles into holes or chinks of rocks, in search of crabs. Now Schneider observed a very young octopus seize a hermitcrab. The hermitcrab covers the shell in which it takes up its abode with stinging zoophytes. Stung by these the octopus immediately recoiled and let its prey escape. Subsequently it was observed to avoid hermitcrabs. Older animals of the same species managed cleverly to pull the crab out of its house without being stung.

* See bk. i., ch. ii., § 8 Acquirement of Meaning § 9 The Various Modes of Specific Reproduction. The examples which follow in the present section will serve to give definiteness to the somewhat vague exposition of the earlier chapter.

+Op. cit., pp. 4041.

Persistence with varying effort is in itself a learning by experience, although it is in the first instance a learning by present experience rather than by past. But it is also a most important precondition of profiting by past experience. Repetition of trials with variation of procedure is a sort of perceptual experiment. The results of previous experiment determine and facilitate future action, inasmuch as unsuccessful modes of procedure are gradually eliminated and successful modes alone survive. I quote from Dr. Wesley Mills' valuable papers* on the "Psychical Development of Young Animals" a very good illustration of this process. The method of Mills was to keep a very careful diary of the behaviour of young animals from their birth. The following entries occur in the register of his observations of a kitten. 26th day: The kitten "leaves its box and goes to a part of the room where there are some bookshelves, the lower ones of which are not completely filled with books, but hold other things. The mother follows it. The kitten is put back into its box. . . . 27th day: On getting out of box the kitten starts on a little run for the bookshelves. It was taken from among the objects on the shelf, turned towards the box and given a few taps. It ran on to the box and got into it. . . . The kitten continues to show a strong desire to get to the bookshelves. . . . 28th day : . . . About 5 p.m. the entrance to the bookshelf was barred up. The kitten first tries every part of the barricade, then pushes in the curtain — cries with vexation — climbs upon a box near — leaps from this on the curtain, holding on with the claws. After trying again and again, desists, and after a few moments returns to the attack. At last she gives it up, returns to her box, settles down and sucks her mother, and then soon after falls asleep. 30th day: It makes many attempts to get into the bookshelf, and at last succeeds. . . . 31st day : In the evening it is found behind the barricade of the bookshelf sleeping on some books. It is taken out, but works its way back again. It finds getting out difficult, but perseveres. . . . 32nd day: ... It tries the bookshelf barricade, but, not succeeding, gives up and sits in its box near by and grooms itself well. Later it makes a more determined attempt on the barricade, and with success. It has difficulty in getting out; but soon goes in again and remains from half to threequarters of an hour. . . . 33rd day: Found behind the barricade this morning before daylight, when, trying to prevent its advance in a certain direction the kitten evades me by running under a rockingchair where it is partly hidden. . . . Though the bookshelves were closed by a curtain tacked on them, the kitten managed to get in, though I do not know how. . . . 35th day : ... It scrambles into the bookshelf by a new way and at much greater height."

* Recently collected in part iii. of a book entitled: The Nature and Development of Animal Intelligence. New York: The Macmillan Company, 1898. Price, $2.00.