DEATH-FEIGNING IN TERRESTRIAL AMPHIPODS. 1 



S. J. HOLMES. 



The instinct of feigning death is extensively distributed through- 

 out the animal kingdom and appears to have arisen sporadically in 

 several groups of animals. It crops out here and there among un- 

 related forms in such a manner that it is evident that the instinct 

 has arisen independently along many different lines of descent. 

 Various theories of the origin of this instinct have been advanced, 

 but it is by no means evident that the method of its development 

 has been in all cases the same. While at Wood's Hole, Mass., 

 during the past summer my attention was drawn to the death- 

 feigning of the large terrestrial amphipods which occur there in 

 great numbers on the beach, and I was led to study the behavior 

 of these animals with the end of ascertaining, if possible, how their 

 peculiar instinct may have arisen. The family Orchestiidse, to 

 which the terrestial Amphipoda belong, is partly terrestrial and 

 partly aquatic, and the terrestial forms are, as a rule, confined to 

 within a short distance of the seashore where they live in an 

 atmosphere heavily charged with moisture. The instincts of the 

 terrestrial Orchestiidae which adapt them to their peculiar habitat 

 must have arisen through certain modifications of the behavior 

 of their aquatic relatives ; and as there are several terrestrial and 

 two aquatic species of this family found at Wood's Hole the 

 attempt was made to gain light upon the problem by a compara- 

 tive study of the behavior of these different forms. I was unable 

 to study the behavior of one of the large sand-fleas, Talorchestia 

 megalopJithalma, as I failed to obtain any specimens in a living 

 condition. The allied species T. longicornis is much more abun- 

 dant at Wood's Hole and may easily be obtained in any desired 

 quantity. It is the only species observed in which the death- 

 feigning instinct is clearly shown, but the other species, as will 

 appear below, manifest the same fundamental peculiarity, though 

 in an altered form. 



1 From the Zoological Department of the University of Michigan, Ann Arbor, 

 Mich. 



191 



