Principles of Heredity 193 



Professor Weldon is at liberty to suggest there is a fair 

 chance that Mendel and all who have followed him have 

 either been the victims of this preposterous coincidence not 

 once, but again and again ; or else persisted in the same 

 egregious and perfectly gratuitous blunder. Professor 

 Weldon is skilled in the Calculus of Chance : will he 

 compute the probabilities in favour of his hypothesis ? 



Ancestry and purity of germ-cells. 



To what extent ancestry is likely to elucidate dominance 

 we have now seen. We will briefly consider how laws 

 derived from ancestry stand in regard to segregation of 

 characters among the gametes. 



For Professor Weldon suggests that his view of ancestry 

 will explain the facts not only in regard to dominance and 

 its fluctuations but in regard to the purity of the germ-cells. 

 He does not apply this suggestion in detail, for its error 

 would be immediately exposed. In every strictty Mendelian 

 case the ancestry of the pure extracted recessives or 

 dominants, arising from the breeding of first crosses, is 

 identical with that of the impure dominants [or impure 

 recessives in cases where they exist]. Yet the posterity of 

 each is wholly different. The pure extracted forms, in 

 these simplest cases, are no more likely to produce the 

 form with which they have been crossed than was their 

 pure grandparent ; while the impure forms break up again 

 into both grand-parental forms. 



Ancestry does not touch these facts in the least. They 



I may perhaps be pardoned for failing to discover it, since the tabula- 

 tions are not prepared with this point in view. Reference to the 

 original records would soon clear up the point. 



B. 13 



