LIGHT REACTIONS OF TERRESTRIAL AMPHIPODS 335 



Specimens were collected on the beach south of the Cliff 

 House, San Francisco, during the months of January, February 

 and March. In the dry sand the burrows were often from six 

 to eight inches deep, while in the moist sand they were usually 

 not more than three or four inches from the surface. The large 

 specimens lie curled up and motionless, and remain so for a 

 few seconds, sometimes half a minute, after being taken out 

 of the sand. The smaller ones are more active and seem aroused 

 by the disturbance of the moving sand about them. Most of 

 the Orchestias are easily caught as they crawl out of the up- 

 turned sand. On account of their color and stillness when first 

 dug up, they readily escape the eye, and would get away if 

 they burrowed down instead of coming to the surface. They 

 run quickly over the sandpile out to the shore, where they 

 begin to burrow, usually in depressions in the sand or against 

 bits of wood or other objects. They apparently run in the 

 direction of dark objects. I have often made individuals follow 

 my foot in various directions, and burrow against the side of it. 



0. traskiana were collected on a small beach at Alameda. 

 They live under wet seaweed and collections of rubbish, a little 

 above the high water line. Here they are found in great num- 

 bers during the day. When the grass or rubbish is lifted, they 

 drop quickly to the ground and glide under cover, always away 

 from the direction of the light. When unable to escape this 

 way, they hop rapidly over the sand and hide under objects 

 they come in contact with. In habits and reactions the species 

 is similar to the eastern O. agilis upon which Dr. Holmes worked. 



In order to find some connection between the habits of life 

 of the two species and their modes of response to light and 

 other stimuli under varying conditions, it might be well to define 

 their chief differences, both in structure and in ways of life. 



First: Differences in habitat. — 0. pugettensis lives in the sand, 

 burrows, and probably has little or no light during the day. 

 0. traskiana lives under seaweed, seldom burrows in its native 

 habitat, though it does burrow in confinement when it has 

 nothing but sand to live in. It lives in a region of greater mois- 

 ture than that of 0. pugettensis. 



Second: Differences in general structure. — 0. pugettensis is 

 about two or two and a half times as large as the adult male 



