TRANSMISSION OF ACQUIRED CHARACTERS. 397 



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 by 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 caterpillars 

 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 been indirectly produced by the 

 surroundings. One may reasonably complain when compelled to 

 repeat again and again these elements of knowledge and of thought 

 upon the causes of transformation ! 



Any one who remembers these things, and is aware of the 

 countless number of purposeful characters which cannot possibly 

 depend upon such direct influences, will be very cautious in yielding 

 to any single instance which at first sight appears to be the direct 

 consequence of external conditions. If Detmer had been thus 

 cautious he would hardly have written the following sentence as a 

 resume of the physiological experiments on plants which have been 

 already alluded to : ' In certain cases it is possible, as we have seen, 

 to artificially modify the anatomical structure of certain parts of 

 plants. In such cases the relation between the structure and the 

 external influences is undoubtedly clear: the latter act as the 

 cause ; the anatomical structure of the members of the plant 

 is the consequence of this cause.' A little more logic would 

 have prevented the author from expressing such an opinion, 



