TABLE VII. REACTIONS TO VERTICAL COLORED LIGHT

	Group 1						Group 2						Group 3
Animal no.	13	37	41	43	44	Sum	21	27	36	38	52	Sum	54	56	58	60	62	Sum	Sum Total
Blue	17	22	14	25	29	107	11	21	26	27	26	111	26	32	26	28	10	122	340
White	23	18	26	15	11	93	29	19	14	13	14	89	14	8	14	12	30	78	260
Green	17	26	11	21	29	104	21	27	30	7	26	111	29	31	26	10	9	105	320
White	23	14	29	19	11	96	19	13	10	33	14	89	11	9	14	30	31	95	280
Yellow	25	21	12	20	35	103	12	20	34	25	29	120	19	20	9	28	22	98	321
White	15	19	28	20	15	97	28	20	6	15	11	80	21	20	31	12	18	102	279
Red	37	33	23	22	28	143	21	30	30	33	22	136	32	37	26	33	28	156	435
White	3	7	17	18	12	57	19	10	10	7	18	64	8	3	14	7	12	44	165
Black	23	20	1	28	34	106	9	12	25	40	32	112	25	32	18	34	16	125	343
White	17	20	39	12	6	94	31	28	15		14	88	15	8	22	6	24	75	257
Black	20	15	13	27	37	112	16	11	16	27	24	94	36	40	18	29	29	152	358
Red	20	25	27	13	3	88	24	29	24	13	16	106	4		22	11	11	48	242
Black	20 [236]	25	26	20	32	123	22	15	39	40	32	148	33	22	34	34	11	134	405
Blue	20	15	14	20	8	77	18	25	1		8	52	7	18	6	6	29	66	195
Red	25	17	28	18	8	96	3	15	21	28	20	87	21	13	15	14	28	91	274
Blue	15	23	12	22	32	104	37	25	19	12	20	113	19	27	25	26	12	109	316
Red [237]	21	27	22	10	36	116	13	40	24	21	28	126	22	25	18	21	16	102	344
Blue	19	13	18	30	4	84	27		16	19	12	74	18	15	22	19	24	98	256

The most striking feature of the table is the marked predominance of the red over the white. Here the red reaches 73% of the total number of reactions, and inspection shows that this predominance is uniform not only through the groups but even for the individuals. The constancy of this reaction and the fact that it is so much more frequent than the one to the black as compared with the white, would lead one to expect that the red would have the higher percentage in the combination black-red. Such, however, is not found to be the case, although it does happen with one group. If the arrangement of our color-scale in accordance with increasing intensity of stimulus were correct, we should expect a gradually increasing predominance in reactions to colored light over those to white in the first five pairs. Instead of this we find that green and yellow stand nearest to the white, blue and black come next and are almost equal, while red is very much higher than any. In the pairs black-red and black-blue the red holds its predominance over the blue at about the same rate as in the second pair of the direct comparison, red-blue. The wide individual variations, however, in all these reactions to colored light, except perhaps in the case of red-white, indicate that there is nothing very regular, stereotyped, or mechanical about them. The most that can be said is that in a general way the red end of the spectrum furnishes a less intense stimulus to negative reaction than the blue.

A tendency to habit formation was noticed during the course of these experiments, and it is possible that this may have influenced the results somewhat. Many individuals apparently formed a habit of going to a certain corner as soon as they were reset at the centre. The positions in which they were set were varied and they were headed in different directions, but within a minute after they were released in the middle of the box they would be found in their favorite corner. This was especially the case with no. 38 in Table VI, and I think accounts in some measure for the persistent avoidance of the white. In no case did this continue throughout the whole series, but would sometimes be noted for two or three days at a time in the case of an individual. What were the controlling factors in this habit formation, the means by which orientation and recognition were effected, I was unable to determine.

3. Reactions to Objects

In no case did an animal give any sign of perceiving stationary objects in its path or of avoiding them in any way that could be referred to a visual stimulus. When the animal approached an obstruction there was no hesitation in the movement until the object was touched. Usually even when the antenna had touched the object the animal did not stop, but continued until the contact of the chelæ or even of the rostrum made further movement in that direction impossible.

With moving objects the case was quite different. Here the condition and disposition of the individual animal seemed to be the deciding factors. Often when the animals were trying to climb out of a shallow pan in which they were kept in the experimenting-room, raising a finger or holding out a pencil would be sufficient to make them stop or even start back into the pan. Nor was this response occasioned by any change in the intensity of light, such as that caused by a shadow falling on the animal, for they would react to a movement made on the opposite side of them from the window. In fact, no. 56, the most active in response to moving objects, seemed to react more vigorously to a motion made on the opposite side than when it was made between him and the light. Whenever a person came near the aquarium he and one or two others would take an attitude of defence, and would "face about" to correspond to any movement the person made toward one side or the other. When in the pan mentioned above, any movement of a person within two or three yards of him usually called forth a reaction on his part, and if the pan were placed on the table and the person moved slowly round it, the animal turned with the person, making a complete circuit of the pan.

Reaction to a smaller moving object, however, was not so marked. A black object, 20×8×8 cm., was suspended above the middle of the pan so that if set swinging it would just pass over the top. When it was pulled to one side the animal responded slightly, but after the first swing he seemed to pay no more attention to it. When the operator stepped out from behind the screen, the animal was as keen in its response as before. The experiment was now tried of allowing the object to approach from one direction while the operator moved to a position at right angles to its line of movement. Without hesitation the animal moved so as to keep fronting the operator, without paying any attention to the movement of the smaller object, although this was much nearer.

These observations on the reactions of the crayfish to stationary and moving objects are in line with the conclusions of Plateau [238] and Exner [239] drawn from observations on other Arthropods. It is Exner's belief that the compound eye is a visual apparatus which is almost worthless for detecting the forms of objects, especially if these objects are stationary, but that it may furnish a very keen perception of moving objects.