i86 COLOUR IN NATURE chap. 



changing tints of the hapless cuttles which the storms 

 of spring cast upon the beach. To those who have 

 not, no learned talk of chromatophores will suggest 

 the delicate rosy flush which comes and fades as one 

 touches the sensitive skin. 



The cuttles of our own shores are chiefly remark- 

 able for their changing tints rather than for their 

 brilliancy, but some tropical forms display very 

 bright colours. Thus Octopus pictus is of a yellowish 

 colour with spots "suffused with shades of the 

 richest ultramarine blue, each spot having a light 

 centre and a dark annular border " (Saville Kent). 

 According to Agassiz the deep-sea cuttles are usually 

 brown or purplish-brown. 



2. Colours of Shells. — The fact that most shells 

 are distinguished by their rich and beautiful colour- 

 ing is familiar enough ; their variety and beauty of 

 marking has endeared them alike to the savage, the 

 child, and the artist. Brightness of colour is most 

 common among the shallow-water forms, especially 

 of the tropics ; deep-sea forms tend to be pale in 

 colour, but often possess an iridescent sheen absent 

 from those living in shallow water (Agassiz). Many 

 shells are coloured on the inner surface as well as the 

 outer, and the colouring-matter is rarely uniformly 

 diffused, being most frequently arranged to form 

 patterns and markings. According to Dr. Woodward, 

 " those which are habitually fixed or stationary (like 

 Spondylus and Pecten pletironectes) have the upper 

 valve richly tinted whilst the lower one is colourless." 

 In some cases the mantle is coloured and marked in 

 the same way as the shell. In lanthina the upturned 

 base of the shell is coloured by the violet pigment 



