194 s - J- HOLMES. 



in a different situation on the beach from that occupied by the 

 the species of Talorchestia. The little O. agilis is found in 

 countless numbers beneath the piles of seaweed near the water's 

 edge. This species, as its name implies, is exceedingly active. 

 When disturbed it jumps very rapidly and to such lengths that 

 capturing the creature is an exceedingly difficult undertaking. 

 An enemy which could easily catch the large Talorchestias would 

 find the attempt to capture 0. agilis an unprofitable pursuit. 

 0. agilis generally continues hopping until it alights in a place 

 where it can readily get under some object or wedge itself 

 between bodies, so that it secures contact on a considerable sur- 

 face of its body. Contact seems to exercise a peculiar influence 

 upon this organism, a sort of hypnotic effect apparently, which 

 induces it to flex its body, bend the antennae downward and lie 

 quiet. The body and antenna? are not so strongly flexed as in 

 the death-feigning of Talorchestia, but the same actions are per- 

 formed though not carried so far. When lying thus 0. agilis 

 may be disturbed slightly without performing any movement, but 

 an attempt to pick it up or push it about will cause it to quickly 

 "come to" and hop away in the most lively manner. This 

 instinct of O. agilis to get into close contact with solid objects is 

 an expression of the strong thigmotactic tendency found among 

 amphipods in general. It is a tendency especially marked in the 

 aquatic representative of the Orchestiidae, Allorchestes liitoralis. 

 This species is commonly found under or among stones quite 

 high up on the beach above the range of any of the other aquatic 

 species, thereby showing an approach toward a terrestrial habit. 

 When taken out of the water it is able to perform the exceptional 

 feat of walking upright without falling upon its side, although 

 this is accomplished with some difficulty, and of making leaps 

 into the air like its terrestial relatives. When disturbed it usually 

 moves away by gliding on its side, a movement very common 

 among amphipods which is performed by alternately flexing and 

 extending the abdomen. The efforts are continued until they 

 bring the creature into some niche or crevice where the contact 

 sought for is obtained ; then it curls up and lies quiet. The 

 thigmotactic reactions of amphipods keep these animals among 

 the seaweeds and rocks where they secure .protection and obtain 



