494 'Journal of Comparative Neurology and Psychology. 



motion. When it has gone as far toward the light as it can it 

 settles down preferably in a position of longitudinal orientation. 



When a crab that is facing the light is subjected to very strong 

 illumination it will often raise its body so as to stand supported on 

 the tips of its claws. If the Hght is withdrawn a short distance the 

 body comes to rest again upon the bottom of the dish. The crab 

 may be made to repeat this act many times by causing the light 

 to approach and recede. The behavior of the animal is apparently 

 the involuntary result of the increase in the tension of the leg mus- 

 cles brought about by strong illumination. 



Similar increase in muscular tone by light is shown in the be- 

 havior of the eye-stalks. When a fiddler is seized the eye-stalks 

 are drawn back into the orbits and tightly held there. If, how- 

 ever, the crab is brought very close to a strong light the eye-stalks 

 are erected. If the animal is removed a little further from the 

 light the eye-stalks are pulled back into their orbits again. When 

 brought into strong light the crab is apparently no longer able to 

 hold the eye-stalks down and they come up in spite of the instinct 

 to hold them in a protected situation. If the cornea of one eye 

 is blackened over usually only the unblackened eye rises upon 

 exposure to strong illumination, but the blackened one sometimes 

 does so to a greater or less extent, owing perhaps to the fact that 

 the two eyes usually make associated movements. 



The experiment of crossing the eye-stalks was tried in order to 

 see what effect would be produced on the animal's reactions to 

 light. The eye-stalks of the fiddler crab are long and they may 

 readily be crossed like the parts of a letter X and tied in the middle. 

 Crabs treated in this way show great confusion in their reactions 

 to visual stimuH. When approached they give signs of alarm and 

 frequently run directly towards the source of danger. When a 

 light is moved suddenly they often run towards it instead of away 

 as they usually do from all moving objects. Normal phototaxis, 

 however, is mainly destroyed. The crabs neither go directly to- 

 ward or away from the hght with any regularity; in fact, they seem 

 to pay httle attention to the light, owing perhaps to the discomfort 

 of their unusual predicament. There is no definite reversal of pho- 

 totaxis, which I thought might occur under the circumstances, 

 although there is often a reversal in the responses tomovingobjects. 

 The crabs' actions, however, are hesitating and uncertain; often 

 they move a distance one way and then in another as if the result 



