VII.] TRANSMISSION OF ACQUIRED CHARACTERS. 409 



it as an instance which, if we assume it to be correct, further 

 illustrates my views upon the phenomena presented by the 

 Thuja-shoot. 



The two other facts brought forward by Detmer as proofs of 

 the transforming power of external influences can be explained 

 in precisely the same manner. These instances are— the fact 

 that Tropaeohtm when grown in moist air produces leaves with 

 anatomical characters different from those produced when the 

 plant is grown in dry air ; and the differences in the structure 

 of the leaves of many plants, according as they have been 

 grown in the sun or shade respectively. Such diiVerences do 

 not by any means afford proof of the direct production of 

 structural changes by means of external intUiences. How 

 would such an explanation be consistent with the fact that the 

 leaves are, in all these cases, changed in a highly purposeful 

 manner ? Or is it assumed that these organs were so con- 

 stituted from the beginning, that they are compelled to respond 

 to external conditions by the production of useful changes ? 

 Any one who made such an assertion nowadays, or who even 

 thought of such a thing as a possibility, would prove that he is 

 entirely ignorant of the facts of organic nature, and that he has 

 no claim to be heard upon the question of the transformation 

 of species. The very first necessity in any scientific question 

 is to gain acquaintance with that which has been thought and 

 said upon the subject. And it has been frequently shown that 

 whole groups of useful characters cannot b}^ any possibility 

 have been produced by the direct action of external influences. 

 If a caterpillar, which hides itself by day in the crevices of the 

 bark, possesses the same colour as the latter, while other cater- 

 pillars which rest on leaves are of a green colour, these facts 

 cannot be explained as the results of the direct influence of the 

 bark and leaves. And it would be even less possible to explain 

 upon the same principle all the details of marking and colour 

 by which these animals gain still further protection. If the 

 upper side of the upper wings of certain moths is grey like the 

 stone on which they rest by day, while in butterflies the under 

 side of both wings which are exposed during rest exhibits 

 analogous protective colours, these facts cannot be due to the 

 direct influence of the surroundings which are resembled, but. 

 if they have arisen in any natural manner, they must have 



