54 Journal of Comparative Neurology and Psychology. 



by two oesophageal branches with the central nerve cord, which 

 is represented principally by a single large thoracic ganglion or 

 concrescence of ganglia. The thoracic portion of the nervous 

 system is, however, symmetrical. The mandibles, or the third 

 pair of appendages, crushing jaws, the right of which is larger, 

 the maxillae and the maxillipeds all receive nerves. The nerv- 

 ous system is therefore in general so constructed that it would 

 seem at least reasonable to expect that associations might be 

 formed. 



Expcrivioital 



The systematic experiments by which the association be- 

 tween the "constructs" of two sense fields, taste and vision, 

 was established, and a "reconstruction" or reproduction subse- 

 quently shown possibly to take place, were preceded by various 

 preparatory observations, some of which were made in the sum- 

 mer of 1902. For instance, it was then shown that the Hermit 

 is remarkably thigniotactic , for when a shell inhabited by a crab 

 is suspended at the distance of about twice the diameter of the 

 shell from the floor of the aquarium, the animal is thereby made 

 decidedly uncomfortable, protrudes nearly its entire body, feels 

 about, and usually leaves its shell, especially if there is a vacant 

 shell near by. Suspended at the height of from eight to ten 

 inches the crab will remain in the shell until it dies. They are 

 also somewhat rheotactic. New shells thrown into the aquarium 

 are soon examined and accepted at what would sometimes seem 

 to be a disadvantage. This constant "desire" for change, to- 

 gether with both a great natural rapacity and pugnacity, are in- 

 deed indications of a strenuous life even among Hermits. 



Both that series of observations upon which special empha- 

 sis is placed in this paper, and that preliminary one which 

 showed that the method adopted would probably lead to satis- 

 factory results, were made with a very simple apparatus and in 

 a very simple way. A number of crabs which had been kept 

 in an ordinary laboratory glass jar aquarium about twenty inches 

 in diameter, were made to go into a darkened portion of this 

 that they might get their food, which consisted of a freshly 



