CRUSTACEA OF THE SEASHORE iii 



tract into the centre of the chromatophore, forming 

 a minute and hardly visible speck, or it may spread 

 out into the branching filaments, forming a distinct 

 spot of colour. Each chromatophore may in some 

 cases contain several colours of pigment, and these 

 may expand or contract independently of each other, 

 so that a whole series of changes may be produced by 

 a single chromatophore. In the larger Crabs and 

 Lobsters the visible colour of the animals depends 

 on pigment in the shelly exoskeleton, which is thick 

 enough to hide the chromatophores in the living 

 tissues underneath, and no very rapid or considerable 

 changes are apparent ; but in the smaller forms, in 

 which the exoskeleton is thin and translucent enough 

 to allow the underlying colours to appear through it, 

 the changes in the chromatophores may produce 

 striking effects. Thus, Fritz Miiller describes a 

 species of Fiddler Crab of the genus Gelasimus, in 

 which the hinder part of the carapace was brilliantly 

 white, but five minutes after the Crab was cap- 

 tured it had changed to a dull grey. Many other 

 cases of colour change have been described, but 

 most remarkable and the most fully studied is that 

 of the Prawn, Hippolyte varians, which is very 

 common on our own coasts, and has recently been 

 the subject of a very elaborate series of researches by 

 Professors Keeble and Gamble. The specimens of 

 this Prawn show *'a bewildering variety of colour 

 and of colour-pattern"; they may be uniformly 



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