Colouration in the Invertebrata. 53 



wealth of colour to be found in these animals gives us a very 

 important opportunity of studying decoration, where it first appears 

 in profusion. 



One of the first points that strikes even a casual observer is that 

 amongst the sea-anemonies the colouration is extremely variable, 

 even in the same species and in the same locality. This is in 

 strong contrast to what we generally find amongst the higher 

 organisms, such as insects and birds ; for though considerable 

 variation is found in them, it does not run riot as in the anemonies. 

 It would almost appear as if the actual colour itself was of minor 

 importance, and only the pattern essential ; the precise hue is not 

 fixed, is not important, but the necessity of colour of some sort 

 properly arranged is the object to be attained. Whether this idea 

 has a germ of truth in it or not, it is hard to say, but when we take 

 the fact in connection with its occurrence just where opacity begins, 

 connecting this with the transparency of the lower organisms, and 

 the application of vivid colour to their internal organs, one seems 

 to associate the instability of the anemony's colouring with the 

 transference of colour from the interior to the exterior. Certain it 

 is, that vivid colour never exists in the interior of opaque animals ; 

 it is always developed under the influence of light. The white 

 bones, nerves and cartilages, and the uniform red of mammalian 

 muscles, are not cases of true decorative colouring in our sense of 

 the term, for all bodies must have some colour. All bone is practi- 

 cally white, all mammalian muscle red, but for these colours to be 

 truly decorative, it would be necessary for muscles of apparently 

 the same character often to be differently tinted, just as the 

 apparently similar hairs on a mammal, and scales on an insect, are 

 variously painted. This we do not find, for the shaft-bones and 

 plate-bones, and even such odd bones as the hyoid are all one 

 colour ; and no one would undertake to tell, by its hue, a piece of 

 striped from a piece of unstriped muscle. Decorative colouring 

 must be external in an opaque animal ; it may be internal in a 

 transparent one. 



The connection thus shown between decoration and transparency 

 seems to suggest that hypodermal colour is the original, and 

 epidermal the newer scheme : that the latter was derived from the 

 former. This agrees with Haagen's shrewd hint that all mimetic 

 colour was originally hypodermal. Certain it is that the protective 



