24 Papers from the Marine Biological Laboratory at Tortitgas. 



darker. At 7'' 45 a. m. it was much darker, showing a distinct plaid 

 pattern, while the other ocypoda was still as light in color as at the beginning 

 of the experiment. These results I consider as evidence that the stimulus 

 given to the eye by light is an important factor in bringing out the color- 

 pattern, since the temperature was practically constant throughout the experi- 

 ment. It might be claimed that disturbances in the nervous condition of the 

 specimen affected the results, but in the light of other observations this does 

 not seem probable. 



Experiment X. A specimen with a very dark color-pattern was used 

 and an attempt was made to bring about a color change by frightening it. 

 The crab was stimulated several minutes by moving the hand in front of it. 

 This caused the specimen to run about very vigorously, but there was no 

 change in color. This method of stimulating the crab was continued until 

 it showed signs of exhaustion, but still there was no change in color. When 

 it was subjected to a strong electric shock two of the ambulatory appendages 

 were broken off, but even this had no effect on the color-pattern. Finally 

 the ocypoda was etherized for 2 minutes until it was perfectly quiet, and 

 then allowed to revive, but this brought about no change in color pattern. 



The results obtained in Experiments IV, V, VI, VII show conclusively 

 that the high temperature on the surface of the sand, which is a result of the 

 exposure to the direct sunlight, brings about a proximal migration of the 

 dark pigment under the carapace of Ocypoda (plate 4). Accordingly the 

 following two experiments were tried, in order to determine if the direct 

 sunlight would cause a blanching of the carapace when the temperature was 

 kept comparatively low. 



Experiment XI. An ocypoda which showed a dark color-pattern and 

 which had been kept in the diffuse light of the laboratory (temperature of 

 air 33 C.) was used. It was placed in a dish filled with sea-water and 

 covered with a glass plate. The outside of the dish was then covered with 

 a piece of heavy cloth saturated with alcohol (unfortunately no ice was at 

 hand) and the whole thing was put in the direct sunlight on the sand at 

 2^ 04"" p. m. The evaporation of the alcohol kept the temperature of the 

 water at 35 C. At 2^ 35" p. m. the specimen was still almost as dark as at 

 first. The slight loss of color was probably due to the 2 increase in 

 temperature. 



Experiment XII. Using the same individual, the above experiment was 

 repeated after removing the cooling cloth {2^ 40"! p. m.). At 2^ 56" p. m. 

 the temperature of the water was 45 C. and the specimen had become ven' 

 light. 



Experiment XIII. The ocypoda used in Experiments XI and XII was 

 brought into the laboratory and placed in a shaded place {2^ 56"" p. m. ; 

 temperature of air at 33 C.). At 3" 11" p. m. it had regained its original 

 dark color. 



Experiment XIV. Experiment XI was repeated under the same con- 

 ditions, except that the specimen was put in the darkness of the photographic 

 dark-room. Although the temperature was kept at 35 C. by the above 

 cooling device, the crab soon lost its color-pattern and dark color, a change 

 undoubtedly due to the absence of a light stimulus on the eyes. 



Often during the above experiments individuals were observed to grow 



