COLOURS OP AVATER-MITES. 1239 



mimicry would be, of course, only relative. For instance Piersig 

 quotes Foi'bes, who found that fish did not entirely refuse to eac 

 Water-mites, and gives as his own observation that Ranatra 

 seized and sucked mites without hesitation (3), but does not state 

 whether these were the natural enemies of the mites. Before 

 any generalization can be made about the colours of Water-mites, 

 more information is required about their associations, together 

 with experiments in which their natural enemies are used. 

 Mr. Soar states that many mites vary in colour individually a 

 great deal (e. g. Fiona rufa Koch). It is qviite likely that the 

 colours of other mites than those described here may have some 

 difierent signiricance. 



In conclusion it may be pointed out that many Land-mites are 

 bright scarlet, and no experiments appear to have been done on 

 them. 



6. SUSIMARY. 



1. Ecological observations are described which make probable 

 the existence of Avarning coloration and Aliillerian mimicry 

 among certain species of Hydrachnidae. 



2. Experiments are described which show that these are 

 distasteful to and recognized by Sticklebacks (Gasterosteus 

 ■aculeatus). 



3. There is evidence that scarlet is the colour best remembered 

 by these fish. This makes the evolution of such a set of 

 Miillerian mimics more easy to understand. 



4. Other evidence is given in support of these conclusions. 



Works Quoted. 



1. HiGGiNS, PI. H. 1873. Notes by a Field-naturalist in the 



Western Tropics. Liverpool ; p. 46. 



2. Maxwell, H. British Fresh-water Fishes. London ; p, 83. 



3. Piersig, R. 1900. " Deutschlands Hydrachniden." Zoologica, 



vol. xxii. p. 32. 



4. PouLTO^, E. B. 1887. Proc. Zool. Soc. p. 238. 



5. Saunders, ,T. T. 1918. Proc. Camb. Phil. Soc. vol. xvii. 



p. 236. 



6. Shelford, Y. E. 1913. Animal Communities in Temperate 



America. Chicago; p. 144. 



7. Soar, C. D. 1921. Journ. Photomicrographic Soc. vol. x. 



No. 2. 



8. White, G. M. 1919. J. Exp. Zool. vol. xxvii. p. 443. 



82* 



