LXIII 



became manifest. Darwin himself in his later years toned down his views in 

 this respect and others have continued this process so that at present the expression 

 " struggle for existence " is not meant to imply much more than a general 

 term for the obstacles of all kinds with which every being has to contend in 

 the course of its life, without invariably being of so fierce and aggressive a 

 character. The doctrine of natural selection is not, however, based on the 

 words " struggle for existence " but on their meaning and when, therefore, this 

 no longer corresponds to the old drastic definition, this fierce, agressive 

 character implied by it, can no longer be assigned to natural selection, nor 

 the great influence originally attributed to it and assumed to play such an 

 important role in the theory of mimicry. This assumption nevertheless retains 

 currency in this theory although being devoid of scientific basis. 



On the other hand Mr. Jordan takes no account of the views I have 

 published several years ago concerning colour evolution ; besides the theory of 

 mimicry he discusses, it is true, some different views as to the alleged mimetic 

 phenomena but is silent on this subject, notwithstanding the fact that it is just 

 this theory which affords quite a simple explanation of all the cases of resem- 

 blance which he considers so remarkable, although it must be admitted that 

 his argument would certainly thereby be considerably weakened. In mimetic 

 phenomena colours play the chief role, but as long as one only possesses 

 confused ideas concerning their existence — as long as one does not grasp, 

 for instance, that pigmental colours form a physiological unit governed by 

 definite rules of development — one will be unable to form a clear judgment 

 on these phenomena. A study of colour evolution alone enables us thoroughly 

 to understand the nature and progress of evolutionary phenomena and will 

 induce any one who reflects on the subject to come forth from among the great 

 host of naturalists, whom I had in mind when I repeatedly stated that since 

 Darwin's time one meets continually and everywhere the term "evolution", 

 but that this is by no means the case with persons who possess some clear 

 notion as to its nature. It is only through this study, moreover, that one 

 becomes acquainted with its exceedingly uneven progress and that one thus 

 acquires a much truer insight as to the nature of variation, which plays so 

 important a role in present day biological problems. Thus the nature of 

 dimorphism and polymorphism will be understood in quite a different sense than 

 is mostly the case at present. A new factor has arisen in the scientific study 

 of biological phenomena and amongst these that of mimicry; this factor has 

 to be refuted or admitted but where it is simply ignored no claim to a scien- 

 tific handling of the subject can be made. 



While, therefore, fully admitting the justice of several observations and 



