VI COLOURS OF CRUSTACEA AND ECHINODERMA 137 
Associated probably with the presence of this 
pigment we find numerous bright-coloured integu¬ 
mentary pigments, which may be of the nature of 
derivatives, as well as complex pigments like ante- 
donin and pentacrinin whose relations are more 
doubtful. 
Another point of contrast with the Crustacea is 
the prevalence of dark pigments, which, though most 
characteristic of Holothurians, tend to appear more 
or less frequently in the other groups. 
