XIV 



studied in the caterpillars of the Sphingidae; after which I published it in the 

 first of the above-mentioned works. Several years ago the matter had already 

 been noticed by Prof. Weismann, who considered it, however, as a phenomenon 

 of mimicr}'. Later on I think I have been able to establish the colour-evolution 

 not only among many other orders of insects, but also among birds and mam- 

 mals and even in respect to man. But its full significance as a gradually ad- 

 vancing process of atrophy I have only learned to understand in the study of 

 the imagines of the Lepidoptera ; the course of this process I can only show 

 distinctly as far these imagines are concerned. 



In this way an entirely different insight may be obtained into the Lepidoptera 

 in general as well as into the Rhopalocera in particular, than is the case when 

 such knowledge fails. Many so-called facts of mimicry are in the first place 

 explained by it in a natural way. Also the fact that the colour of both sexes 

 in a species of butterflies may strongly differ, which is incorrectly and without 

 any foundation taken for a secondary sexual phenomenon, though it is simply 

 the result of the circumstance that the process of the colour-evolution does 

 not advance equally in both sexes and that, therefore, one sex proceeding 

 further, has changed more than the other. Further the astonishment with 

 which a few years ago Dr. Oudemans stated that the castration of c? cater- 

 pillars of OcNERiA DisPAR L. has no influence at all on the colour of the but- 

 terflies emerging from them. Just so many phenomena that are at present 

 simply attributed without foundation to heat, cold, dryness, dampness and all 

 other kinds of climatical causes, these influences not being explained in a com- 

 prehensible manner. Indeed such influences exist, but nothing gives us a right 

 to attribute such a great significance to them ; because the real cause is not 

 known, words are used which only represent hollow meanings. So it is for a 

 great part with the so-called local forms and especially with the conception 

 which has been emphasized these latter years about forms of the dry and of 

 the rainy season in the tropical countries, a conception which is understood 

 with European weakness of comprehension according to the nature of the dif- 

 ferences between winter and summer in Europe, so that even in collections 

 they are indicated as summer and winter forms. A terrible exaggeration in 

 this respect nowadays prevails among Lepidopterologists. 



The difference between the dry and the rainy season of the tropics must 

 not at all be considered in the same way and so strongly separated as winter 

 and summer in the temperate zones. Though it is said that Dr. Brandes 

 was the first to mention this fact, it is De Niceville, without doubt, who has 

 most of all drawn the attention of entomologists to the differences, which were 

 said to arise from these causes among butterflies; it is certain at least that 



