of Heredity 33 



that the characters may be carried by the gametes in any 

 proportion from zero to totality, just as some substances 

 may be carried in a solution in any proportion from zero 

 to saturation without discontinuous change of properties. 

 That this will be found true in some cases is, on any 

 hypothesis, certain ; but to prove the fact for any given 

 case will be an exceedingly difficult operation, and I scarcely 

 think it has been yet carried through in such a way as to 

 leave no room for doubt. 



Conversely, the absolute and universal purity of the 

 gametes has certainly not yet been determined for any 

 case ; not even in those cases where it looks most likely 

 that such universal purity exists. Impairment of such 

 purity we may conceive either to occur in the form of 

 mosaic gametes, or of gametes with blended properties. 

 On analogy and from direct evidence we have every right 

 to believe that gametes of both these classes may occur in 

 rare and exceptional cases, of as yet unexplored nature*, 

 but such a phenomenon will not diminish the significance 

 of observed purity. 



We have now seen the essential nature of the Mendelian 

 principles and are able to appreciate the exact relation in 

 which they stand to the group of cases included in the Law 

 of Ancestral Heredity. In seeking any general indication 

 as to the common properties of the phenomena which are 

 already known to obey Mendelian principles we can as yet 

 point to none, and whether some such common features 

 exist or not is unknown. 



There is however one group of cases, definite though 

 as yet not numerous, where we know that the Mendelian 



* It will be understood from what follows, that the existence of 

 mosaic zygotes is no proof that either component gamete was mosaic. 



B. 3 



