VI COLOURS OF CRUSTACEA AND ECHINODERMA 119 



the smaller and more delicate forms. The resem- 

 blances between shrimps, sand-hoppers, shore-crabs, 

 etc., and the localities which they respectively haunt 

 are too patent to need emphasis, and phenomena of 

 this nature are exceedingly common in the group. 

 In many cases the colours vary in harmony with 

 the environment, but this can only occur in forms in 

 which the epidermis is the important agent in colora- 

 tion, and is then due to the sensitiveness of the 

 chromatophores. We find this in the shore-crab in the 

 young stage, and in many of the small sessile-eyed 

 Crustacea, such as Idotea and Caprella. The prawn 

 Hippolyte, according to M. A. E. Malard, is green on 

 green seaweed, brown on Fucus, red on red seaweed, 

 and transparent among Antennularia and Sertularia. 

 Experiment in artificial environment showed that 

 this form is red in darkness, emerald-green in bright 

 light, and brown in semi-obscurity, which seems to 

 prove that it is the intensity of light rather than its 

 colour which is of importance in effecting colour- 

 change. Pouchet found that prawns (e.g. Leander 

 serrator) turned brownish-red in vessels with black 

 bottoms, and if then transferred to white vessels 

 became yellow, passing through a stage in which 

 they were bright blue. Pouchet stated that the 

 brownish-red colour was due to a combination of a 

 bright red colour due to chromatophores and a 

 soluble blue pigment. When the prawns were re- 

 moved to a white dish, the chromatophores slowly 

 contracted and allowed the blue colour to become 

 apparent. As the contraction proceeded the blue 

 pigment gradually disappeared, and the ultimate 

 yellow colour was produced by the contracted 



