Il6 REPORTS ON INVESTIGATIONS AND PROJECTS. 



passage branching off from it and sometimes communicating with the exterior. 

 The latter passage is used only for escape when the crab is pursued by an 

 enemy. In digging its burrow Ocypoda carries the sand out with its legs, 

 holding them so that they make a sort of basket, and upon reaching the sur- 

 face the load is disposed of by a quick movement of the legs, which may 

 throw the sand for a distance of a foot or more. Molting takes place during 

 the spring and early summer, and probably occurs at the bottom of the deep 

 burrows. 



The males are somewhat larger than the females, and on account of their 

 fighting are more scarred. The breeding season probably extends throughout 

 the summer and occurs just after molting. 



Ocypoda feeds both during the day and night, and is a scavenger; but 

 small live fish are also eaten with apparent relish. While the olfactory sense 

 to some extent guides these crabs to their food, the eyes, feeling, and taste 

 seem to be the principal factors. Any small object dropped upon the sand 

 within 4 or 5 feet of them when the observer is hidden is usually immediately 

 seized for food. In this case it is not the appearance that suggests it is food, 

 but the fact that the object has moved. 



On Loggerhead Key, Ocypoda seems to have but two enemies, namely, the 

 gray snapper and the land crab. The birds do not molest it, and there are 

 no mammals excepting man on the island. 



While Ocypodse frequently fight among themselves, fatalities do not gen- 

 erally occur, and it is only seldom that an individual is found with one of 

 its chelae missing. They often attack and kill the land crab, which is pro- 

 tected with a much harder shell than its own. The older Ocypodse nearly al- 

 ways have fractured ambulatory appendages, the result of pinches received 

 while fighting. 



Often, when an individual is surprised, so that it runs a danger in trying 

 to get back to its burrow, it will settle down in a little hollow and partly 

 cover itself with sand, usually leaving the eyes exposed. Occasionally the 

 young Ocypoda will lie flat upon the sand, remaining perfectly still and allow 

 man to approach within a foot or two. The adults are not conspicuous 

 when observed at a distance of 30 or 40 feet, but when 8 or 10 feet away they 

 are easily seen. In the young, however, the color of the carapace is chalky 

 gray, making them almost indistinguishable from the sand when the observer 

 is a few feet away. 



Ocypoda travels sideways with surprising speed, and is able to move for- 

 ward almost as fast. It can walk backwards with difficulty, but when a quick 

 movement in this direction is necessary it usually jumps. 



While Ocypodae live well submerged in sea-water, they are unable to exist 

 long without it. The hot sun shining directly upon them in confinement will 

 soon cause death. They do not go into the ocean to feed, but only to re- 

 plenish the water in their gill chambers, or to escape from enemies, and in 

 no case do they venture into deep water. It seems to be necessary for the 

 young to change the water in the gill chambers more frequently than for the 

 adults, and their burrows are made correspondingly closer to the water-line. 



Ocypoda is usually able to return to its burrow quickly and with consider- 

 able accuracy from a distance of 15 or 20 feet. While the eyes are probably 

 a factor contributing to this accuracy, the sensitive ambulatory appendages 

 undoubtedly aid by the sense of touch. 



