12 Darbishire, Lazvs of Heredity. 



will be encountered in establishing the invalidity of 

 Mendel's Law as facts accumulate. 



To discover a definition of the second class is not so 

 easy. To my mind, there are two perfectly distinct things 

 included under the one term Mendelism. One is belief 

 in the existence of character-units in the germ, and in the 

 thesis that these units are pure in respect of the characters 

 which they represent. The other is the hiethod by which 

 the extent, separateness, and transmission of these units 

 is discovered. The first may be called the Mendelian 

 theory, the second the Mendelian method — which is 

 the application of the experimental method to the study 

 of heredity. I think that both these things are implied 

 when the term Mendelism is used ; and whether they are 

 or not — and it does not in the least matter — I believe 

 that the Mendelian method will do as great service, in 

 accounting for the phenomena of heredity, as that parti- 

 cular theory which Mendelians happen to be employing 

 at the moment. 



For I think that it must be evident to anyone who 

 has followed closely the Mendelian work of the last few 

 years that, while the method which workers of that school 

 have employed has remained the same, the actual theories, 

 by testing the validity of which they have sought to attain 

 their end, have been from time to time considerably 

 modified. This procedure, of course, makes it difficult for 

 those who wish to criticise or base statistical calculations 

 on the theory itself. Pearson comments on it in these words: 

 " The original Mendelian theory has been replaced by 

 what are termed " Mendelian Principles." In this aspect 

 of investigation the fundamental principles propounded 

 by Mendel are given up, and for each individual case a 

 pure gamete formula of one kind or another is suggested 

 as describing the facts. This formula is then emphasized, 



