For Group IX. the conditions were again reversed, this time the Left passage being closed.  Here the first trial was one of long and careful exploration, but thereafter no more mistakes were made in the first series, and in the group of fifty tests there were only five wrong choices.

The fifth column, R. L. and L. R., of Table II. contains cases in which the subject started toward one side and then changed its course before reaching the partition.  In Group III., for instance, when the Left passage was closed, the subject started toward the Left seven times, but in each case changed to the Right before reaching the partition.  This is the best evidence of the importance of vision that these experiments furnish.

The first experiments on habit formation proved conclusively that the crawfish is able to learn.  The observations which have just been described prove that the labyrinth habit is not merely the following of a path by the senses of smell, taste or touch, but that other sensory data, in the absence of those mentioned, direct the animals.  So far as these experiments go there appear to be at least four sensory factors of importance in the formation of a simple labyrinth habit:  the chemical sense, touch, vision and the muscle sense.  That the chemical sense and touch are valuable guiding senses is evident from even superficial observation, and of the importance of vision and the muscle sense we are certain from the experimental evidence at hand.

[Illustration:  FIG. 3.  Path taken by crawfish while being trained to avoid the left passage.  Marks along the glass plate and partition indicate contact by the antennae and chelae.]

Of the significance of the sensations due to the ’direction of turning’ in these habits the best evidence that is furnished by this work is that of the following observations.  In case of the tests of Table II. the subject was, after 100 preliminary tests, trained by 250 experiences to escape by the Right-hand passage.  Now, in Groups III. to VII., the subject’s usual manner of getting out of the closed passage, when by a wrong choice it happened to get into it, was to draw back on the curled abdomen, after the antennae and chelae had touched the glass plate, and then move the chelae slowly along the Right wall of the partition until it came to the upper end; it would then walk around the partition and out by the open passage.  Fig. 3 represents such a course.  In Group VIII. the Right passage was closed, instead of the Left as previously.  The first time the animal tried to get out of the box after this change in the conditions it walked directly into the Right passage.  Finding this closed it at once turned to the Right, as it had been accustomed to do when it came in contact with the glass plate, and moved along the side of the box just as it did in trying to get around the end of the partition.  The path taken by the crawfish in this experiment is represented in Fig. 4.  It is very complex, for the animal wandered about more than fifteen minutes before escaping.