of Heredity \ 7 



1900, the same author's paper in Proc. R. S. vol. 66, 1900, 

 p. 140, or the extensive memoir (pubd. Oct. 1900), on the 

 inheritance of coat-colour in horses and eye-colour in man 

 (Phil. Trans. 195, A, 1900, p. 79), will not need to be told 

 that the few words I have given above constitute a most 

 imperfect diagram of the operations of that law as now de- 

 veloped. Until the appearance of these treatises it was, 

 I believe, generally considered that the law of Ancestral 

 Heredity was to be taken as applying to phenomena like 

 these (coat-colour, eye-colour, &c.) where the inheritance 

 is generally alternative, as well as to the phenomena 

 of blended inheritance. 



Pearson, in the writings referred to, besides withdrawing ' 

 other large categories of phenomena from the scope of its 

 operations, points out that the law of Ancestral Heredity 

 does not satisfactorily express the cases of alternative 

 inheritance. He urges, and with reason, that these classes 

 of phenomena should be separately dealt with. 



The whole issue as regards the various possibilities of 

 heredity now recognized will be made clearer by a very brief 

 exposition of the several conceptions involved. 



If an organism producing germ-cells of a given constitu- 

 tion, uniform in respect of the characters they bear, breeds 

 with another organism* bearing precisely similar germ- 

 cells, the offspring resulting will, if the conditions are 

 identical, be uniform. 



In practice such a phenomenon is seen in ^r0-breeding. 

 It is true that we know no case in nature where all the 

 germ-cells are thus identical, and where no variation takes 

 place beyond what we can attribute to conditions, but we 



* For simplicity the case of self-fertilisation is omitted from this 

 consideration. 



B. 2 



