iv GABRIEL KOCH'S EXPERIMENTS 149 



hour, as in Dr. Fickert's experiment only the one surrounded 

 with green was almost as light as that on the white surface, 

 and the one entirely excluded from light, although it became 

 distinctly darker in that time, even after four hours could only 

 be called brown, not dark. 



We have thus the remarkable fact that the change of 

 colour in frogs begins at once, but only slowly reaches its full 

 extent, and that it also takes place slowly in toads, which 

 entirely agrees with my interpretation of the change in 

 favour of adaptation without selection. 



PARTICULAR FACTS WHICH PROVE THE INFLUENCE OF NUTRI- 

 TION AND OTHER EXTERNAL CONDITIONS ON THE VARIATION 



AND FORMATION OF SPECIES IN LEPIDOPTERA 



After I had in vain applied to various experts for trust- 

 worthy personal observations upon the effect of the nutrition 

 of the caterpillars on the variation of Lepidoptera, and had 

 concluded the preceding pages, a book was brought to my 

 notice entitled The Indo- Australian Lepidoptera, etc., with a 

 Discussion of the Origin of Colours in Pupce, by Gabriel Koch 

 (second edition, Berlin, 1873). This work contains some facts 

 of much importance for my arguments, and its author, on the 

 basis of these facts, expresses some views on the origin of 

 varieties which completely harmonise with mine. 



Koch states that his attempts to influence the colours of 

 Lepidoptera by the feeding of the caterpillars date from the 

 year 1832, when he succeeded in producing in Chelonia Hebe 

 either fiery or dull red on the under wings, and in bringing 

 out more strongly either the black marking or the white 

 ground alternatively by feeding with different plants. 1 

 Other successful experiments were made on Chelonia Caja, 

 and Nemeophila plantaginis. 2 



1 Published in a paper on Die Raupen und Schmetterlinge der Wetterau. 

 a Vid. G. Koch : Die Schmetterlinge des sMwestlichen Deutschlands. 



