20 Papers from the Marine Biological Laboratory at Tortugas. 



tliaii three days. The base of the eye-stalks is undoubtedly one of the most 

 vital spots, and it is probably true that in nature the eyes are never pinched 

 off without causing death. 



I have seen many hundred ocypodas both at Loggerhead Key and Beau- 

 fort, North Carolina, and while I have often found specimens with one of 

 the chelae or one or two of the ambulatory appendages missing, I have 

 never seen an individual with even one eye gone. Those ocypodas that had 

 both eyes cut off did not react in any way to light or shadow cast upon them, 

 and there is scarcely any doubt that the eyes are the only organs that are 

 sensitive. Notwithstanding the severe shock resulting from the amputation 

 of the eyes, individuals were often found that would be feeding at the end 

 of 24 hours. 



The effect of painting the eyes with a mixture of lampblack, shellac, and 

 chloroform was also tried. When several coatings of this mixture were 

 put on, these organs were not sensitive to light. It was found that imme- 

 diately after the painting individuals were quiet, but that very soon they 

 became more active and assumed the defensive attitude (plate i, fig. c). 

 As Bethe (1895, 1897) has observed in the case of Carciiius, they were well 

 able to protect themselves from normal individuals. On land they were 

 much more sensitive to tactile stimuli than ordinarily, and in the aquarium 

 they were much more sensitive to the vibrations of the water produced by 

 striking the glass than normal ocypodas. 



The angle of compensation when a crab was tilted was somewhat less 

 than the normal, confirming the observations of Clark (1896) and Prentiss 

 (1901) for the fiddler-crab and those of Lyon (1899) for the crayfish. 

 The blackening of the eyes seemed to have no effect on the maintenance of 

 equilibrium and did not prevent the ocypodas from running about in a nor- 

 mal manner when stimulated. 



The most evident change in the behavior under these abnormal condi- 

 tions was the lack of reaction to a sudden increase or decrease in the inten- 

 sity of light, the absence of any reaction to moving objects and the failure 

 to approach objects as they ordinarily do when the eyes are not painted. 



Several experiments were tried to determine if the eye of Ocypoda re- 

 acted to one color more than to another. For this 18 atherinas were used; 

 6 were stained red, 6 were stained blue, and the rest were left unstained. 

 These were thrown alternately to an ocypoda, but there was no special 

 difference in the behavior toward the different ones. 



An attempt was made to see if they would form an association between 

 colors and food made distasteful in some way. Many experiments using 

 stained atherinas soaked in the acid juice of the lime were tried, but these did 

 not give any results indicating an association of color with distasteful food. 



Quite a number of experiments with red and violet color-filters made of 

 celloidin were tried, but these vielded no definite results. 



