ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 351 



*• Crustacea. 



Behaviour of Ocypoda arenaria.* — R. P. Cowles has made a study 

 of the interesting Brachyuran, Ocypoda armaria, the " sand-crab " of 

 the Atlantic coast of the Southern States. He found that the adult 

 made two kinds of burrows. One consists of a single tunnel extending 

 downwards in the sand for three or four feet. The other is shorter, 

 and has a passage branching off from it, used for escape. Young crabs 

 make burrows only a few inches deep. Breeding apparently took place 

 in the spring and early summer. The sand-crab is a scavenger and a 

 cannibal. It was not conclusively shown that it was stimulated by the 

 odour of food, but experiments seemed to point to this. 



The eyes are, for crustacean eyes, highly developed ; they are sensi- 

 tive to considerable differences in the intensity of light : they do not 

 react to different colours ; they aid greatly in the search for food, and 

 in the accuracy of locomotion. The colour-pattern seen through the 

 carapace of Ocypoda changes in intensity under different conditions of 

 temperature and light. In the absence of light, when the temperature 

 is anywhere between 22° and 45° C, and undoubtedly when it is even 

 lower or higher, a light coloration occurs. Generally in diffuse light, 

 and even in direct sunlight, a dark coloration appears, provided the 

 temperature is not too high. Usually at low temperatures a dark 

 coloration appears, provided the eye is stimulated by light. At high 

 temperatures, above 35° C, a light coloration is the rule, and it occurs 

 independently of light. 



No indication of audition was observed. The so-called " auditory 

 organs " are equilibrating organs. There is a stridulating ridge on the 

 palm of its large chela. Any sound which it may make is probably not 

 heard by any other individuals, but the vibrations produced are 

 probably felt by other Ocypodas. 



The tactile sense is well developed. With the body orientated in a 

 fixed position, the animal can move in practically any direction. It 

 runs with a considerable degree of accuracy, and undoubtedly has a 

 sense of position and distance. In locomotion these crabs are guided 

 by differences in the lighting of surfaces, by tactile stimuli, by differences 

 in muscular effort, and by the stimulation of the equilibrating organs 

 resulting from a tilting of the body. The sand-crab lives on land, and 

 only goes to the water to moisten the gills. It usually dies if exposed 

 to direct sunlight without water for more than four hours. It can live 

 in the burrows without fresh sea-water for at least forty-eight hours. 

 The " Aufbiium reflex " described by Bethe, is an attitude of defence. 

 The animal often hides from man by simply settling down and th rowing- 

 sand over its body. It is sometimes found in a resting or " sleeping " 

 condition, when it does not react to many of the ordinary stimuli. The 

 death-feigning reaction is exhibited under certain conditions. There 

 is evidence that the animal has the power of forming definite associa- 

 tions and habits. 



* Publications Carnegie Inst. Washington, No. 103 (1909) pp. 1-41 (4 pis. 

 and 10 figs.). 



