22 Papers from the Marine Biological Laboratory at Tortugas. 



pattern. Three of these were then put in a glass dish and placed in the 

 direct sunlight on the white sand. Ten minutes later these had lost nearly 

 all their color, showing almost no markings. The other one was kept in the 

 diffuse light of the laboratory and did not change in color. It had the same 

 dark pattern the next day. These observations left no doubt that the color- 

 pattern under the carapace was subject to considerable change when placed 

 under different conditions of light, heat, or moisture, and experiments were 

 then undertaken to determine what factors brought this change about. 



Experiment I. Three small oc\podas, quite light in color, were taken 

 fnim the trap and placed in the box with colored windows at ^^ 15 p. m. 

 The box was kept in the bright light near a window until 4^ 50" p. m., when 

 it was found that the crabs had not changed in color. So far as these ex- 

 periments were concerned there was no indication that the colored windows 

 had anything to do with the formation of a color-pattern. However, it is 

 not claimed that careful experiments with color-screens might not show that 

 certain parts of the spectrum may be more effective in bringing about color 

 changes than others. After the specimens were removed from the box they 

 were put into sea-water and kept in the laboratory, where they began to turn 

 dark at once. They were then removed to a dry dish, where they continued 

 to grow darker. 



Experiment II. Two rather dark ocypodas were exposed to the direct 

 sunlight for 15 minutes and became very light in color. They were then 

 put into a dish of sea-water and placed in a rather shaded part of the labora- 

 tory (8'" 12" a. m.). A dark plaid pattern soon made its appearance, after 

 which the crabs were put in the direct sunlight on the white sand still im- 

 mersed in sea-water (S*" 22 a. m.). At 8'' 30 a. m. they were much lighter 

 in color and at 8'' 49 a. m. they were almost colorless. The specimens 

 were then put in a photographic dark-room {& 50 a. m.), still immersed 

 in sea-water. To my surprise (believing at the time that bright light was 

 -the cause of blanching) at 10'^ 45 a. m. they were still almost colorless. 

 However, upon being put in a dry dish and placed in a shaded part of the 

 laboratory, they became dark after a few minutes. 



These experiments show that the appearance and disappearance of the 

 color-pattern is not a simple process, but that it may be brought about by 

 one or several factors. 



Experiment III. In this experiment the same individual was used that 

 was kept in the laboratory in Experiment I. It was dark in color. It was 

 immersed in sea-water and exposed to the direct sunlight (8 a. m.). At 

 gh 23m a. m. the specimen had not changed in color to any appreciable de- 

 gree and at 8'' 30 a. m. it was possibly a little lighter. The crab was then 

 placed in a dry dish (8'' 31" a. m.) and left in the sunlight. As would be 

 expected, at 8'' 35'" a. m. the specimen was still light. At 8'' 40 a. m. it 

 was put in a dish covered with a black tray and placed in the photographic 

 dark-room. When examined at 10'' 45 a. m. it was found to be still devoid 

 of a color-pattern, as in the case of Experiment II. When the individual was 

 put in sea-water and placed in a shaded part of the laboratory it became 

 quite dark after a few minutes. 



Experiment IV. A rectangular glass dish, 35 cm. in length, 25 cm. in 



