374 EXPERIMENTAL STUDY OF INHERITANCE 



No one can, of course, at present say that these "simple 

 equations " will apply to the introduction of fresh blood into 

 a herd of cattle, but the time has come for more daring ex- 

 periment on Mendelian lines. It might obviously happen that 

 the " fresh blood " (B) introduced was quite incompatible with 

 the pure-bred (A), and the progeny was an undesirable freak. 

 But do not such casualties happen under the present instinctive 

 or empirical regime followed by most breeders ? 



§ 7. Other Experiments on Heredity 



Our survey of cases must be supplemented by reference to 

 the works of Bateson, T. H. Morgan, Punnett, De Vries, and 

 others ; but we have said enough to show,— (1) that Mendelian 

 phenomena are well illustrated in certain cases — e.g. peas, mice, 

 rabbits, poultry, snails ; (2) that in other cases, while there are 

 clear Mendelian phenomena according to some observers, dis- 

 crepant results have been reached by others — e.g. silk-moths ; 

 (3) that in other cases, while there are hints of Mendelian pheno- 

 mena, the results cannot be readily interpreted in conformity 

 with Mendelism — e.g. pigeons. 



It seems to us that the results depend in part on whether 

 there are or are not sufficiently well-marked contrasted unit 

 characters in the two parents. When the differences between 

 the two original parent-types are not crisply definable in terms 

 of contrasted unit characters, the conditions of Mendelian in- 

 heritance are not afforded, and we have to fall back upon the 

 old-fashioned description of the inheritance as " blended " or 

 " particulate " or " reversionary," and so forth. 



It must be clearly noted that Mendelian phenomena are not 

 known except in certain cases of hybridisation. They chiefly 

 occur in the inbreeding of the hybrid progeny of two well-j 

 marked varieties or " elementary species," We do not know! 



