34 Papers from the Marine Biological Laboratory at Tortugas. 



my walks along the beach. The body always rests on the sand, the legs are 

 relaxed and stretched out, and the eyes are down in their sockets. Unless the 

 sand is jarred too much by the approach of the observer, they lie perfectly 

 still and do not react to changes in light intensity caused by the movement 

 of an object in front of them. They may be even picked up before they 

 show signs of activity. Upon one occasion a piece of meat on the end of a 

 reed was moved within about 5 cm. of the mouth-parts, but this brought forth 

 no reaction nor did the crab react when the meat was held as close to the 

 mouth-parts as possible without touching them. When, however, the ap- 

 pendages of the mouth were touched by the food, they began to move 

 slowly and then faster; after this the eyes came up, the ambulatory ap- 

 pendages assumed the position necessary for locomotion, and finally the 

 chelae seized the meat. 



While Ocypoda does not normally exhibit what has been called the 

 death-feigning reaction, or, as Bethe (1897I has called it, in the case of 

 Carcinus, the " Starrkrampf reflex," it does so sometimes when placed 

 upon its back and held in that position for a minute or so. 



MEMORY. 



Since the appearance of Rethe's (1898) classical paper on the nervous 

 system of Carcinus manas, in which he compares this crustacean to a reflex 

 machine and denies it the ability to learn, several papers have appeared 

 which furnish abundant proof that some crabs are able to profit by ex- 

 perience and are even capable of forming habits. Yerkes (1902) investigat- 

 ing Carcinus granulatits, Yerkes and Huggins (1903) studying the crayfish 

 Cambarus affinis, and Spaulding (1904) working on the hermit-crab Eupa- 

 giirus longicarpus, have found that these Crustacea form associations. 



I hoped that Ocypoda would be a favorable subject for a quantitative 

 study of habit formation, but as far as my experiments have been carried 

 this does not seem to be the case. Ocypoda, we have seen, is a very active 

 crustacean ; its eyes are very sensitive when compared to those of other 

 crabs ; it is easily frightened, and when in this condition either runs away 

 rapidly or remains perfectly still, failing to behave normally; when placed 

 in a labyrinth with a solid bottom it usually scampers away from the hand that 

 has released it and then often settles down in a corner without attempting to 

 escape, or tries in vain to dig a burrow ; failing in this it tries to climb ; when 

 the bottom of the labyrinth is made of sand it usually digs a burrow, goes 

 down in it, plugs up the entrance, and stays there for a considerable time. 



For the reason just mentioned it has been found very difficult to devise 

 labyrinths which would be satisfactory, and the data accumulated on the 

 length of time required for individuals to escape are probably not very 

 trustworthy information concerning the rapidity with which Ocypoda forms 

 a habit. 



