Group.  Number of    L.    R.   Time in   Tests. 
Animal.       Per cent.   Seconds. 
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

Group.  Number of    L.    R.   Time in   Tests. 
Animal.       Per cent.   Seconds. 
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 chelae 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.

Chelae.  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

Since these measurements indicate slightly greater size on the right it is very probable that we have in this fact an explanation of the tendency to turn to that side.