101 



NOTE ON THE 

 PROTECTIVE DEVICES OF THE GENUS HIPPOLYTE. 



BY JAMES HOENELL. 



a. The colour adaptability of the adult H. varians to the hue of its 

 environment. 



b. The significance of the plumose hairs of H. fascigera is mimetic 

 and not primarily sensory. 



During the past summer (1897) I took advantage of an unusual 

 abundance in the Jersey rock-pools of the little iEsop's Prawns, Hippolyte 

 (Virbius) varians, Leach, and H. fascigera, Gosse, to carry out some 

 experiments I had long contemplated relative to the protective coloura- 

 tion of these crustaceans. 



That the former species is very variable in colour and that the 

 colours are plainly of protective value are well-known facts ; thus 

 Professor Herdman in 1893 described in the " Sixth Annual Eeport of 

 the Liverpool Marine Biology Committee," four variations of H. varians, 

 each agreeing in hue with the colour of its special habitat. He put 

 forward four alternative possibilities to account for such variability, 

 thus : — 



1. The colours noted may represent four distinct varieties which do 

 not interbreed, keep to their own special habitat, and produce young 

 of their own colours. 



2. Or, there may be no permanent varieties, but the young may 

 have great adaptability and assume the hue of the habitat they find 

 themselves in and keep to this for the rest of their lives. 



3. Or, this adaptability may be retained throughout the rest of their 

 lives and the adults may change hue upon change of environment. 



4. Or, the young may be very variable in tint and then by the 

 action of natural selection, such as do not agree in hue with the sur- 

 roundings will be eliminated. 



He added that he was inclined to regard the last as the most 

 probable explanation. 



Starting my experiments with these possibilities in view, I collected 

 a quantity of both our common local species and isolated the individuals 

 in separate glass vessels, each containing sea-weed of a different hue to 

 that of the prawn. 



The experiments were conclusive and proved Professor Herdman's 

 third alternative suggestion to be the correct one, namely, that the adults 



