Forced Movements, Tropisms, and Animal Conduct

When this pigeon was almost a year old it was pnt into a cage with a female pigeon, hut although the female aroused the sexual instinct of the formerly isolated male the latter did not mate with her, hut mated with the hand of his attendant when the hand was put into the cage, and this continued throughout the season. Thus the memory images acquired hy the bird at an impressionable age and period perverted its sexual tropisms. It is perhaps of more importance to show that memory images may have a direct orienting influence. The chemo- tropic phenomenon of an insect laying its egg on a sub¬ stance which serves as food (for both mother and off¬ spring) and for which the mother is positively chemo- tropic, may he modified, hy an act of associative memory, e.g., when a solitary wasp drags the caterpillar on which it lays its eggs to a previously prepared hole in the ground. The essential part of the instinct, the laying of the eggs on the caterpillar, does, perhaps, not differ very much from the fly laying its eggs on decaying meat; and the solitary wasp may he strongly positively chemotropic for the caterpillar on which it lays the eggs, although this has not yet been investigated. But the phenomenon is complicated hy a second tropism, which we will call the orienting effect of the memory image. As is weU known, the wasp before “going for” the caterpillar digs a hole in the ground to which it afterwards drags the caterpil¬ lar, often from a distance. The finding of this previously prepared hole hy the returning wasp, the writer would designate as the tropistic or orienting effect of the memory image of the location of this hole; meaning thereby that the memory image of the location of this hole makes the animal return to this location. The conduct of these wasps

is familiar to many readers and the writer may be par¬ doned for quoting from a formerly published observation. Ammophilaj a solitary wasp, makes a small hole in the ground and then goes out to hunt for a caterpillar, which, when found, it paralyses by one or several stings. The wasp carries the caterpillar back to the nest, puts it into the hole, and covers the latter with sand. Before this is done, it deposits its eggs on the caterpillar which serves the young larva as food.

An Anmophila had made a hole in a flower bed and left the flower bed flying. A little later I saw an Ammophila running on the sidewalk of the street in front of the garden, dragging a caterpillar which it held in its mouth. The weight of the caterpillar prevented the wasp from flying. The garden was higher than the sidewalk and separated from it by a stone wall. The wasp repeatedly made an attempt to climb upon the stone wall, but kept falling down. .Suspecting that it might have a hole prepared in the garden, I was curious to see whether and how it would find the hole. It followed the wall until it reached the neigh¬ boring yard, which had no* wall. It now left the street and crawled into this yard, dragging the caterpillar along. Then crawling through the fence which separated the two yards, it dropped the caterpillar near the foot of a tree, and flew away. After a short zigzag flight it alighted on a flower bed in which I noticed two small holes. It soon left the bed and flew back to the tree, not in a straight line but in three stages, stopping twice on its way. At the third stop it landed at the place where the caterpillar lay. The caterpillar was then dragged to the hole, pulled into it, and the hole was covered with tiny stones in the usual way.^s*^

It is not enough to say that the animal possesses, associative memory and returns to the hole; we must add that the brain image of the region of the hole becomes the sonrce of a forced orientation of the animal—of an added special tropism—compelling the animal to return to the region corresponding to the image. And the same may he said in regard to the return of the wasp to the caterpillar which had been temporarily deposited at the foot of the tree.

show the addition necessary to the tropism theory to make it include the endless number of reactions in which associa¬ tive memory is involved. The psychiatrist would find it easy to supply numerous examples of this type of forced movements toward certain objects which have left a memory image. Since the writer has not investigated this subject sufficiently he is not in a position to give more than a suggestion for the direction of further work. He is inclined to believe that with this enlargement the trop¬ ism theory might include human conduct also if we realize that certain memory images may exercise as definite an orienting influence as, e.g., moving retina images or sex hormones.

This tentative extension of the forced movement or tropism theory of animal conduct may explain why higher animals and human beings seem to possess freedom of will, although all movements are of the nature of forced movements. The tropistic effects of memory images and the modification and inhibition of tropisms by memory images make the number of possible reactions so great that prediction becomes almost impossible and it is this impossibility chiefly which gives rise to the doctrine of free will. The theory of free will originated and is held not among physicists but among verbalists. We have shown that an organism goes where its legs carry it and that the direction of the motion is forced upon the organ¬ ism. When the orienting force is obvious to us, the motion appears as being willed or instinctive; the latter generally when all individuals act alike, machine fashion, the former when different individuals act differently. When a swarm of Daphnia is sensitized with CO 2 they all rush to the source of light. This is a machine-like action, and many

will be willing to admit that it is a forced movement or an instinctive reaction. After the CO^ has evaporated the animals become indifferent to light, and while formerly they had only one degree of freedom of motion they now can move in any direction. In this case the motions appear to be spontaneous or free, since we are not in a position to state why Daphnia a moves to the right and Daphnia b to the left, etc. As a matter of fact, the motion of each individual is again determined by something but we do not know what it is. The persistent courtship of a human male for a definite individual female may appear as an example of persistent will, yet it is a complicated tropism in which sex hormones and definite memory images are the determining factors. Eemoval of the sex glands abol¬ ishes the courtship and replacing the sex glands of an individual by those of the opposite sex may lead to a complete reversal of the sex instincts. What appears as persistent will action is, therefore, essentially a tropistic reaction. The production of heliotropism by CO 2 in Daphnia and the production of the definite courtship of the male A for the female B are similar phenomena differ¬ ing only by the nature of the hormones and the additional tropistic effects of certain memory images in the case of courtship. Our conception of the existence of ‘‘free will” in human beings rests on the fact that our knowledge is often not suflSciently complete to account for the orienting forces, especially when we carry out a “premeditated” act, or when we carry out an act which gives us pain or may lead to our destruction, and our incomplete knowl¬ edge is due to the sheer endless number of possible com¬ binations and mutual inhibitions of the orienting effect of individual memory images.

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6 Allee, W. C. Further Studies on Physiological States and Rheotaxis ® Allee, W. C. : Certain Relations Between Rheotaxis and Resistance to Potassium Cyanide in Isopoda. J. Exp. Zool., 1914, xvi, 397- 7 Allee, W. C. : The Ecological Importance of the Rheotactie Reaction ^ Allee, W. C., and Tashieo, S. : Some Relations Between Rheotaxis and the Rate of Carbon Dioxide Production of Isopods. J. Animal Behav., 1914, iv, 202-214. Allen, G. D. : Reversibility of the Reactions of Planaria doroto- cephala to a Current of Water. Biol. Bull., 1915, xxix, 111-128.

i2Ari8z, W. H. : On the Connection Between Stimulus and Effect in Phototropie Curvatures of Seedlings of Avena sativa. Proc. Boy. Acad. Amsterdam, 1911, xiii, 1022-1031. 13 Axbnfeld, D. : Quelques observations sur la vue des arthropodes. Arch. Hal. Biol., 1899, xxxi. 1^ Bach, H. : Ueber die Abhangigkeit der geotropischen Pr^entations- und Reaktionszeit von verschiedenen ausseren Faktoren. Jahrb. wiss. Bot., 1907, xliv, 57-123. a The list of literature does not claim to be complete. Aside from un¬ intentional omissions, some of the controversial and amateurpublica¬ tions have not been included.

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18 Bancroft, F. W. : The Control of Galvanotropisna in Paramceciim by Chemical Substances. Univ. Cal. Pub. Physiol., 1906, iii, 21-31. 20 Bancroft, F. W. : The Mechanism of Galvanotropic Orientation in 22 Banta, a. M.:' Experiments on the Light and Tactile Reactions of a Cave Variety and an Open Water Variety of an Amphipod Species. Proc. Soc. Exp. Biol, and Med., 1913, x, 192. 24 Barratt, j. 0. W.: Der Einfluss der Konzentration auf die Chemo- 25 Barrows, W. M. : The Reactions of the Pomace Fly,. Drosophila

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