No. 590] FECUNDITY IN THE DOMESTIC FOWL 105 



Castle, and the advocates of the pure-line concept, reduces 

 itself finally very largely to a dispute over the use of 

 words, if both are discussing the same objective facts or 

 experiments. It is repugnant to the logical faculties of 

 the pure-linists to be told that selection is a cause of new 

 variations. On the other hand, I suspect that this par- 

 ticular use of words, which is offensive to our. camp, would 

 not be deemed absolutely essential to the making of their 

 case by Castle and his followers. Castle's special bete 

 noir appears to be that the pure-linists seem to him to 

 deny the possibility of germinal variation, except it be 

 large in amount (a proper De Vriesian mutation). Xow 

 I am in no wise authorized to speak for the pure-line ad- 

 vocates, but I can say for myself, and I venture to think 

 others would agree, that this contention forms no part of 

 the real, genuine pure-line body of doctrine. The fol- 

 lowers of the pure-line merely have observed in fact that 

 it is not so easy to change all things by a process of selec- 

 tive breeding as it has been to change the pattern of 

 Castle's rats, or the egg production of my fowls. Many 

 characters, and many organisms, when got into a homo- 

 zygous condition exhibit any germinal variation so rarely 

 as to make any change by the selection of such variation 

 impossible within the limits of finite experimentation. 

 Neither J ohannsen nor any followers of his, so far as I 

 am aware, have ever attempted to set any limitations on 

 how big or how little a germinal variation could be. 



