THE COLOUR SCALE IN MARINE ANIMALS. 



BY JAMES HORNELL. 



IN a previous note on colouration (p. 8), I had occasion to chronicle 

 the fact that a chromatic Scale similar to that found in the 

 evolution of flowers, and with which Grant Allen and others have 

 made us so familiar, can be made out in the colouring of marine 

 animals. As the subject is interesting, I may be allowed here to 

 amplify the statement. 



The presumed order of evolution being from white, through 

 yellow, orange, red, and purple to blue, we would expect the more 

 primitive colours — white and yellow — to characterise the more simply 

 organised species in each phylum or great division of the animal 

 kingdom. As complexity in structure progresses, we may naturally 

 look for corresponding advance in the colour scale. The advance 

 will however not be made without purpose ; some powerful reason — 

 warning, mimicry, sexuality, &c. — must be present or the primitive 

 colour will not be forsaken, and again through the working of the 

 great law of atavism or reversion, so soon as the existing cause ceases 

 or waxes faint, the advanced colour will in time be renounced, and 

 the more primitive resumed. 



Blue, the highest grade, is, as we are thus led to expect, seldom 

 found in marine creatures. On our own coasts I can recollect only 

 the sometimes lilac coloured sponge Chalina montagui ; several 

 purple sea-urchins, Spatangus purpureus, Bryssus lyrifer, Strongy- 

 locentrotus lividus, and Sphcerechinus granulans ; some partially 

 blue Copepoda ; the Lobster ; several purple and blue compound 

 Ascidians, and some partially blue fishes. 



These animals are all among the most highly specialized animals 

 of the groups or classes to which they respectively belong. Among 

 the sponges, the Silicispongise, to which Chalina belongs, stands 

 practically at the top — the great complication of the canal system, 

 and the wonderful development of the mesoderm placing this 

 order far in advance of the members of the other great sponge order, 

 the Calcispongiae. These latter, thus characterised by comparative 

 simplicity, are all but entirely white. One only do I know of other 

 colour, Ascetta coriacea, and then the hue, pale yellow or orange, 

 is not even normal, being merely a varietal colouring. 



The sea-urchins are among the most highly specialized of their 

 phylum or indeed of any animals ; the blue splashed Copepod, Ano- 

 malocera pattersoni is among the most highly organized of his order, 

 and the Lobster, again, is in many respects the foremost of our 

 macrourous (long-tailed) crustaceans. As to the Ascidians, there is no 

 question that the species sporting blue and lilac colours are among the 

 most special, for as such are counted the crusting compound Ascidians 



