Habits, Reactions, and Associations in Ocypoda arenaria. 23 



perceptibly darker after removal from water into a dry dish. This color 

 change was undoubtedly due to a decrease in temperature resulting from the 

 evaporation of water from the surface of the specimen. 



Many observations were made on ocypodas living under natural condi- 

 tions. During the middle of the day, when the sun was shining brightly, 

 specimens seen feeding on the sand were usually light in color, but occasion- 

 ally dark individuals were found. These latter had probably just emerged 

 from their cool, shady burrows (the entrance not closed). During the late 

 hours of the afternoon and on cloudy days, however, most of the ocypodas 

 feeding along the beach were dark in color, although occasionally a very 

 light one would be seen. Probably the latter had been buried in a closed 

 burrow which was dark. 



The following interesting observation of the efifect of light on the pig- 

 ment-cells of the eye was made : A small ocypoda was kept in a box, the 

 bottom of which was filled with sand to a depth of 10 cm. There was a 

 crack left between the bottom of the box and one of its sides, into which 

 the direct sunlight shone. The specimen had burrowed to the bottom of the 

 box in such a way as to have one eye exposed to the direct sunlight while 

 the rest of the body, including the other eye, was in comparative darkness. 

 When this individual was taken out the eye which had been exposed was 

 almost devoid of black pigment, while the other one was black as usual. 

 The color-pattern under the carapace, however, was neither very dark nor 

 very light. After 15 minutes in the diffuse light of the laboratory both eyes 

 were as black as usual. 



While no experiments were tried to determine the effects of light and 

 heat on the pigment migration in the retina of the eye, it is probablv true 

 that the blanching in this case was due to the heat of the direct sunlight and 

 not to the light itself. The medium dark coloration of the hypodermis under 

 the carapace may be explained by the facts that the eye was stimulated by 

 light and that the rest of the body was exposed to a medium temperature, 

 two conditions which, according to my experiments, would result in a 

 medium dark coloration. 



DISCUSSION OF RESULTS. 



Brooks and Herrick (1889) working on Alpheus and Palcsmonctcs, P. 

 Mayer (1879) O" Idothea, and Herdman (1894) on Virbius varians find that 

 the stimulation of the eyes by light is an important factor in color change. 

 Malard (1892) tells us that in the case of Hippolyte varians the intensity 

 of the light has an effect on the color, and that in many Crustacea the stimu- 

 lation of the eye by light and the color environment are factors. In Idotea 

 tricuspidata Matzdorff (1882) finds tliat variations in temperature, light, and 

 density of water do not cause color change, but claims that the latter is a 

 " sympatische Wechselfjirbung " which varies with the surroundings. 

 Pouchet (1872), in his work on Palamon and Leander serrator, lavs special 



