542 V. w. (JAMiM-i':. 



Intkoductuky. 



This paper is a continuation of the series hitherto published 

 in conjunction with Professor Keeble (1900-1905), and con- 

 tains a further instahnent of experimental results of a 

 research upon the colour-physiology of the prawn H i ppoly te 

 varians, and the wrasse Crenilabrus in el ops. 'J'he work 

 was carried out by the author during the last three years, in 

 part at the Plymouth Laboratory of the Marine Biological 

 Association, in part at the Millport Marine Station, and also at 

 Manchester University. To the directors of these laboratories 

 and to the staff of the Plymouth and ^lillport Stations, the 

 special thanks of the author are due for the unstinted help 

 which they have always been ready to give. His former 

 colleague, Professor Hickson, has given the author ever- 

 ready assistance and much helpful criticism. 



1. Thk Influenck op Surroundings (Algal Backgrounds) 

 ON THE Colour of Crenilabrus Melops. 



(1) Introductory. 



The immediate object with which this experiment was 

 undertaken was to ascertain whether in the young stage of 

 the fish there was a sensitive period at all comparable to 

 that which is possessed by Hippolyte. I had thought that 

 by exposing the young fish to backgrounds of diversely 

 coloured weeds it would be possible to obtain some light 

 as to the origin of the colour varieties which the wrasse 

 exhibits. 



As in the case of Crustacea these colour varieties may be 

 classed under two heads: First, the individual colour forms, 

 which show a series of more or less marked vertical bars on 

 a variable body colour, and second, the colour phases 

 exhibited by any given individual. 



The Labrida3 offer an exceedingly rich field of research for 



