Harvard Psychological Studies, Volume 1 / Containing Sixteen Experimental Investigations from the Harvard Psychological Laboratory.

by Unknown

For the following experiments the subject was placed on its back on a smooth surface in the air and permitted to turn over in any way it could. Our purpose was to determine (1) whether there was any marked tendency to turn in a certain way, (2) whether if such was not the case a tendency could be developed by changing the conditions, and (3) how alteration in the conditions of the test would affect the turning.

A great many records were taken, but we shall give in detail only a representative series. In Table III., 557 tests made upon four subjects have been arranged in four groups for convenience of comparison of the conditions at different periods of the training process. Each of these groups, if perfect, would contain 40 tests for each of the four subjects, but as a result of accidents II., III., and IV. are incomplete.

TABLE III.

RE-TURNING OF CRAWFISH.

Group.	Number of Animal.	L.	R.	Time in Seconds.	Tests.
		Per cent.
I.	2	22.5	77.5	14.6	40
	3	42.5	57.5	2.6	40
	4	52.8	47.2	4.3	38
	16	44.5	55.5	22.5	45
	—	——	——	——	——
		40.6	59.4	10.8	163
II.	2	28	72	50	43
	3	32	68	6.2	50
	4	—	100	6.8	40
	16	31.3	68.7	39.3	42
	—	——	——	——	——
		22.8	77.2	25.6	175
III.	2	2.5	97.5	46.5	40
	—	—	—	—	—
	4	20	80	5.5	40
	16	41	59	15	49
	—	——	——	——	——
		21.2	78.8	22	129
IV.	2	2	98	41	50
	—	—	—	—	—
	4	32.5	67.5	7.3	40
	—	——	——	——	——
		17	83	24	90

Group I., representing 163 tests, shows 59 per cent. to the right, with a time interval of 10.8 seconds (i.e., the time occupied in turning). Group II. shows 77 per cent. to the right; and so throughout the table there is an increase in the number of returnings to the right. These figures at first sight seem to indicate the formation of a habit, but in such case we would expect, also, a shortening of the time of turning. It may be, however, that the animals were gradually developing a tendency to turn in the easiest manner, and that at the same time they were becoming more accustomed to the unusual position and were no longer so strongly stimulated, when placed on their backs, to attempt to right themselves.

All the subjects were measured and weighed in order to discover whether there were inequalities of the two sides of the body which would make it easier to turn to the one side than to the other. The chelæ were measured from the inner angle of the joint of the protopodite to the angle of articulation with the dactylopodite. The carapace was measured on each side, from the anterior margin of the cephalic groove to the posterior extremity of the lateral edge. The median length of the carapace was taken, from the tip of the rostrum to the posterior edge, and the length of the abdomen was taken from this point to the edge of the telson. These measurements, together with the weights of three of the subjects, are given in the accompanying table.

TABLE IV.

MEASUREMENTS OF CRAWFISH.

	Chelæ.		Carapace.			Abdomen.	Weight.
	Left.	Right.	Left.	Right.	Median.
No. 2,	9.8	10.0	38.2	38.7	47.3	48.1	29.7
No. 4,	7.7	7.7	33.6	33.8	39.4	42.3	17.7
No. 16,	12.5	12.4	37.6	37.6	46.4	53.2	36.2