To test the effect of a change in the conditions, No. 16 was tried on a surface slanted at an angle of 1 deg. 12’.  Upon this surface the subject was each time so placed that the slant would favor turning to the right.  Under these conditions No. 16 gave the following results in two series of tests.  In the first series, consisting of 46 turns, 82.6 per cent. were to the right, and the average time for turning was 17.4 seconds; in the second series, of 41 tests, there were 97.5 per cent, to the right, with an average time of 2.5 seconds.  We have here an immediate change in the animal’s method of re-turning caused by a slight change in the conditions.  The subject was now tested again on a level surface, with the result that in 49 tests only 59 per cent. were toward the right, and the time was 15 seconds.

SUMMARY.

1.  Experiments with crawfish prove that they are able to learn simple labyrinth habits.  They profit by experience rather slowly, from fifty to one hundred experiences being necessary to cause a perfect association.

2.  In the crawfish the chief factors in the formation of such habits are the chemical sense (probably both smell and taste), touch, sight and the muscular sensations resulting from the direction of turning.  The animals are able to learn a path when the possibility of following a scent is excluded.

3.  The ease with which a simple labyrinth habit may be modified depends upon the number of experiences the animal has had; the more familiar the animal is with the situation, the more quickly it changes its habits.  If the habit is one involving the choice of one of two passages, reversal of the conditions confuses the subject much more the first time than in subsequent cases.

4.  Crawfish right themselves, when placed on their backs, by the easiest method; and this is found to depend usually upon the relative weight of the two sides of the body.  When placed upon a surface which is not level they take advantage, after a few experiences, of the inclination by turning toward the lower side.

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THE INSTINCTS, HABITS, AND REACTIONS OF THE FROG.

BY ROBERT MEARNS YERKES.

PART I. THE ASSOCIATIVE PROCESSES OF THE GREEN FROG.

I. SOME CHARACTERISTICS OF THE GREEN FROG.

The common green frog, Rana clamitans, is greenish or brownish in color, usually mottled with darker spots.  It is much smaller than the bull frog, being from two to four inches in length ordinarily, and may readily be distinguished from it by the presence of prominent glandular folds on the sides of the back.  In the bull frog, Rana catesbeana, these folds are very small and indistinct.  The green frog is found in large numbers in many of the ponds and