

FATTY PIGMENTS 161 



star-shaped masses (chromatophores) , which can con- 

 tract to a mere dot, leaving clear interspaces between 

 one mass of pigment and another, or, again, can expand 

 to a radiate form, branching out and filling the skin 

 with a tracery of colouring. In the same way the 

 skins of shrimps and prawns are dotted over w,ith 

 little mobile bags of pigment, now expanded into star- 

 like forms and rendering the animal of a deep brown 

 colour, and anon contracting to as many microscopic 

 black-looking dots, separated by clear interspaces, 

 and the effect of which is to give the shrimp or prawn 

 a transparent and colourless appearance. 



As we go further down in the scale these pigments 

 become still more abundant. They suffuse the skins 

 of most starfish, sea-urchins, sea-cucumbers, and brittle- 

 stars. 



This substance, which in its yellow or red form has 

 such an extraordinarily wide distribution amongst 

 animals, is no less common amongst plants. The 

 green substance of ordinary leaves contains it. In all 

 underground stems, roots, and tubers it is present, 

 though often only in small quantities, as in the turnip, 

 or in a concentrated form as in the carrot. In the 

 fungi it produces most of the brilliant orange, yellow, 

 and red effects that so strikingly catch the eye on 

 leaves, palings, and tree-trunks which are infested by 

 moulds. Even amongst the simplest of all forms of 

 life the bacteria the same pigment is still to be 

 found. From the lowest to the highest forms of plants, 

 from the simplest Protozoon up" to man himself, there 



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