3o8 COLOUR IN NATURE chap. 



elaborate discussion of the possible uses of colour, 

 for we see that it arises apart from usefulness, and 

 ergo may persist apart from usefulness. This is the 

 view put forward in the Evolution of Sex, where the 

 colours of organisms are regarded as expressions of 

 the constitution of the individual. 



3. Mr. Cunningham and Professor Eimer's 

 Theories. — Although the theories as to the origin of 

 colour, adopted on the one hand by Mr. Poulton, 

 and on the other by Mr. Wallace, are widely accepted 

 among biologists, dissentients are not wanting, and 

 are probably on the increase. Among the older 

 theories, that dependent upon the acceptance of 

 Lamarck's factor of an inheritance of acquired 

 characters, has been vigorously maintained by Mr. 

 Cunningham in this country, and Professor Eimer 

 and a numerous school abroad. Professor Eimer's 

 theories of the origin of colours and markings involve 

 especially the conception that in this, as in other 

 respects, evolution is a progression along definite lines 

 determined by laws of growth which are the accumu- 

 lative result of environmental stimuli ; the emphasis 

 is, however, so laid upon the laws of growth that the 

 fact that these involve an inheritance of the effects 

 of environmental influence is apt to be lost sight of 

 The difference between this and the preceding 

 theories is best indicated by a concrete example. 

 We may take the vexed question as to the reason 

 for the absence of pigment in cave-inhabiting animals. 

 According to Mr. Poulton, animals which live in 

 darkness are pale, because pigment would not be 

 visible in these situations ^and is consequently no 

 longer of any use to them ; it is, therefore, no longer 



