MARINE BIOLOGICAL STATION AT PORT ERIK. 37 



adaptability, so that under the influence of their environ- 

 ment they soon assume a protective colouration ; more- 

 over in each generation the action of natural selection 

 will eliminate those most markedly dissimilar to their en- 

 vironment and those which cannot so readily be modified, 

 and this process will go on during the whole of life ; 

 further, the adaptability, or marked susceptibility to the 

 influence of environment, is retained throughout adult life, 

 so that, e.g., a green Virbius from the Zoster a put in a 

 clump of Halidrys can change to a dark brown colour. The 

 change in colour is, of course, due to changes in size, and 

 in the arrangement of the contained pigment granules, of 

 the chromatophores. In a reddish brown Virbius examined 

 on September 6th the integument was seen under the 

 microscope to be richly pigmented with very large stellate 

 and elaborately branched chromatophores containing pig- 

 ment of various colours, such as blue, yellow, red, brown 

 and chocolate, the last three being the most conspicuous. 

 When this specimen was examined again on September 7th, 

 after the 24 hours in green sea-weeds, it was found that 

 all the chromatophores were smaller and less branched, and 

 that the blue and yellow ones were now the most con- 

 spicuous, the red and brown ones being mostly contracted 

 down to little rounded dots. It would be interesting to 

 determine whether here, as in some other cases of similar 

 colour changes, the modification of the chromatophores is 

 due to nerve action and is dependent upon sight, or is the 

 result of the direct action of light upon the integument. 



Swarms of Amphipods. 

 On several occasions during the past year the Biological 

 Station has been invaded by countless numbers of com- 

 mon shore Amphipoda, chiefly Orchestia gammarellus (the 

 shore hopper), accompanied by small black flies and some 



