1925] the relative importanceof vision and the chemical sense in

1925] Vision and Chemical Sense in Anax Larwe 315

THE RELATIVE IMPORTANCE OF VISION AND THECHEMICAL SENSE IN ANAX LARVAE.

CYRIL E. ABBOTT.

University of Wisconsin, Madison, Wis.

General observations and experimental work on the larvm ofAnaxjunius for over a year, seemed to indicate that the responsesof these insects are chiefly dependent on the sense of sight. Thustaking of food, in particular, seems to be the result of reactionsto form and movement. General observation also indicated thatthe chemical sense was correspondingly weak. Although thequestion of image-formation ir/insects has been treated by Cole(1907), Demoll (1910), Forel (1908), and Seitz (1912); and thechemical sense by numerous authorities, including Forel (1908),Kafka (1918), and Lubbock (1888); apparently no work hasbeen done with dragon-fly larvm. Accordingly, two experimentswere made; one to test the reactions of the larvm to form, theother to determine whether or not they would react to thechemical emanations from distant objects. Each experiment isa check on the other, and both are related to prehension.

Reaction to Form.Individual. Positive responses Negative responses

I. Food: 15 oTriangle: 4 7

2. Food: 9 7Triangle: 12

3. Food:Triangle: o 9

4. Food: Io oTriangle: 4 15

5. Food: 9 5Triangle:

6. Food: 8 5Triangle: o 3

7. Food: I3Triangle: o 16

8. Food: IO oTriangle:

9. Food: 9 7Triangle: o 12

IO. Food: II 4Triangle" o 8

316 Psyche [December

Chemical Sense.

was used.the broth.

In ten of the twelve tests a broth made from meal-wormsIn the remaining trials pyridine was substituted for

Individual Positive Negative No responseresponse response. 5 o 6,2. o 4 83. IO

4. 3 85. 4 4 46. o o7. o o8. o o 12

9. :3 8

Discussion.

The larvm were numbered and a record kept of their be-havior. Almost daily, but not always at the same hour, eachinsect was fed a bit of meal-worm (Tenebrio molitor) about threecubic mms. in volume. Every day the insects were stirred witha paper triangle on the end of a needle. The triangle had anarea of about one squre cm. It was at first presumed, becauseof the results of experiments indicating that these animals havesome degree of memory, that learning would simplify the ex-periment; but in this case the larvm gave no evidence of as-sociating either pleasant sensation with the food or an un-pleasant one with the triangles. Probably any tendency to formassociations was inhibited by the complexities of the experiment.

The bove experiment is open to the objection that somechemical sense may have influenced the behavior of the larvre.Nine insects were tested by introducing into the water nearthem a broth made from meal-worms. This was introduced atall possible distances from, and all possible angles to, the insects.Some lrvm moved their mandibles when surrounded by a densecloud of the suspension; most of them seemed totally unawareof the presence of the liquid. This broth was a visible suspension,which probably accounts for the fact that larvae 1 and 9 extendedtheir labi when it was introduced. They gave no responsewhen their eyes were covered with asphaltum.

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