336 DARWINISM TO-DAY. 



sarily a theory of sudden large changes or variations, al- 

 though it is of sudden and fixed ones. It is not based on 

 any belief that sports or large variations are any more 

 numerous, nor of any more worth as the beginnings of new 

 species, than now generally recognised, but it assumes 

 sudden radical changes in the organism which, if not visibly 

 large as regards obvious quantitative conditions, are large or 

 at least comprehensive as regards qualitative conditions. 

 The mutation or variation assumed by the theory of hetero- 

 genesis affects many organs and parts, structurally and 

 physiologically ; it produces a radical change throughout the 

 organism. And this change is the result of an influence 

 wholly intrinsic, inherent, and has no reference to external 

 conditions, except in that the stimulus for it may come partly 

 or chiefly from specially favourable conditions of nutrition. 

 This change is at once definitive and fixed : it is transmitted 

 unimpaired to the offspring of the organism showing the 

 mutation, only the capacity for the production of offspring, 

 i. e., the reproductive fertility, is often weakened. 



Korschinsky's theory and declarations are not based on 

 any very large amount of personal experimentation and 

 observation at least his references to new facts are few and 

 meagre. He gives a short list of old and more or less 

 familiar together with a few new examples of heterogenesis 

 but he does not lend the theory of heterogenesis very much 

 in the way of authority, except in so far as the evidently 

 positive and clear conviction on the part of a biologist of 

 experience and reputable standing of the necessity and truth 

 of such a theory is authority. Korschinsky's conviction is 

 probably based on much observation and experience besides 

 that which he definitely catalogued, but what is needed to 

 carry conviction to others is direct reference to proved, and 

 where possible verifiable, facts of observation and experi- 

 ment. 



The supplying of this demand, to a degree which will 



