Habits, Reactions, and Associations in Ocypoda arenaria. 23 



width and 7 cm. in depth, was divided into two equal parts by a partition in 

 the middle. One of these parts was lined and also covered with black glass. 

 The other part was left without lining except that the side of the partition 

 was covered with white bristol-board. The cover was made of ordinary 

 clear white glass. Sea-water was poured into the dish until it was 2.5 cm. 

 deep and then two crabs with dark plaid patterns were put in — the darker 

 of the two in the light side, the other in the dark side (8'' 35™ a. m.). The 

 dish was then placed in the direct sunlight until 9*^ 47"" a. m. Both were 

 equally light in color. (Temperature of water 45° C. at end of experiment.) 

 The results indicated that heat was the factor which brought about the loss 

 of color, so the following experiment was tried: 



Experiment V. — Two dark specimens of practically the same shade 

 were used. One was placed in a dish of water kept at a temperature of 45° 

 C. (temperature of the water in Experiment IV after exposure to the sun), 

 the other in water whose temperature was 23° C, and both were put in a 

 shaded part of the laboratory ; they were left for 15 minutes, after which the 

 former became decidedly lighter, while the latter did not change. 



Experiment VI. — The same experiment was repeated, except that the 

 temperature of one was kept at 44° C. and the other at 23° C. The result 

 was the same. 



The last three experiments undoubtedly show that a temperature as high 

 as that on the sands of Loggerhead Key will cause a loss of color when the 

 specimen is not exposed to bright sunlight. These results received further 

 confirmation in the following experiment: 



Experiment VII. — Two dark-colored ocypodas were used. At 2" 35™ 

 p. m. one was put in a dry dish over a sand-bath, kept at 36° C, in a shaded 

 part of the laboratory, and the other was placed under the same conditions, 

 except that it was not heated. (Temperature of air 24° C.) At 3 p. m. the 

 former had almost lost its color-pattern, while the latter had not changed. 



Experiment VIII. — A light-colored ocypoda (i) which had its eyes 

 painted with shellac and lampblack (it did not react to shadows) was put 

 in a dish of sea-water and placed in a shaded part of the laboratory at 

 y^ 40™ a. m. Another light-colored one (2), whose eyes were painted (it was 

 not quite as light as the other), was put in the direct sunlight without water 

 C^h 20" a. m.). At y^ SC" a. m. (2) was brought into the laboratory, put 

 in a dish of sea-water, and placed in the shaded part of the laboratory. 

 Crab ( I ) was taken out of the sea-water, put in a dry dish, and then in the 

 shaded part of the laboratory {y^ 56™ a. m.). Finally (2) was taken out of 

 the water and left in the shaded part of the laboratory {^^ 06" a. m.). 

 Throughout these changes neither (i) nor (2) changed in color, and at 

 gh 2im 3 rn they were in the same condition. This experiment aflfords quite 

 conclusive proof that the eye of Ocypoda must receive light stimuli in order 

 to bring about a distal migration of pigment under the carapace, i. e., in 

 order for the color-pattern to appear. 



Experiment IX. — In this experiment two ocypodas whose eyes had been 

 painted 24 hours before were used. (They did not react to light.) Both 

 of the specimens were light in color, although kept in the shaded part of the 

 laboratory (6 a. m. Temperature 23° C). The paint was removed from 

 the eyes of one of the individuals and in less than half an hour it became 



