IV KOCH'S CONCLUSIONS 153 



larger, in Australia smaller. But there are also very large 

 native species in Australia {e.g. the giant hawk-moths Brachy- 

 glossa triangularis and B. Australasise, etc.) Instances of 

 species which become smaller in Australia are Cheerocampa 

 celerio, Sphinx convolvuli, Euchelia pulchra, and many others. 



Koch further discusses the importance of the season of the 

 year in which Lepido]3tera appear, and mentions, after re- 

 ferring to Vanessa Levana, and Prorsa, that the second 

 generation of Argynnis Selene, which takes flight in the 

 height of summer, also has finer and blacker spots and 

 markings than the one which comes out in spring. 



Thus Koch also reaches the conclusion that the origin of 

 permanent varieties is to be ascribed to external influences, 

 and the most important result gained by his work is that 

 he makes it probable that many forms at present considered 

 as species are only similar permanent varieties. It is a re- 

 markable proof of the hold which the idea of the permanence 

 of species has upon systematists, that Koch never once refers 

 to the question whether species might not arise or have 

 arisen in this way, although he supplies instances thereof. 



In the preceding I believe I have proved beyond a doubt 

 that external influences— ^climate, light, warmth, moisture, 

 and differences of food — modify organisms directly, even 

 without the aid of selection, and that inasmuch as the. modi- 

 fications so caused are inherited, they will give rise and must 

 have given rise to new species. I presuppose, however, that 

 the inheritance of characters acquired through the action of 

 external influences is an indisputable fact. 



Chaeacters acquired by Use 



It is a self-evident physiological fact that practice or 

 use strengthens and improves the organs of the body, while 

 disuse causes them to deteriorate. 



