Vaiiaticin and Selectiou; a Keply. 261 



If one objects to averagiug the grades of the offspring, lie may, 

 if he chooses, deal with them unaveraged; they are presented in our 

 tables in such form that each reader may do as he likes about it. 



6. The Hagedoorxs consider their method of recoiding the young 

 by pictures superior to ours of recording them by grades. Having 

 employed both methods extensively, I cannot concur in their view. The 

 picture method is satisfactory, if one is dealing with a small number 

 of observations or those of a preliminary character only, but becomes 

 insupportably laborious when one deals -with large numbers. With such 

 definitely localized areas of white aud black as the hooded rat presents, 

 it is easy to devise a system of standard stages or grades to guide one 

 in classifying the auimals. Even if one pictures every rat (an impossible 

 task, when numbers are large) the day of classifying the young is only 

 postponed thereby. Sooner or later some classification must be made, 

 if quantitative variation is to receive any consideration whatever, if 

 only into the Hagedoorns' categories of "light" and "dark" hooded. 

 Carefully prepared grades allow of more accurate description than such 

 categories, and may subsequently be dealt with statistically, unless like 

 the HAC4EDOORNS one steadfastly refuses to use such tools of investi- 

 gation and insists on making all his excavations with the bare hands, 

 scorning pick and shovel. 



7. A counter criticism. 



In 1911, Dr. Hagedoorn took occasion to criticise briefly (in the 

 Mendel Festschrift) my selection experiments with rats, referring to 

 experiments of his own as a basis for showing the unsoundness of mine. 

 The passage in full is as follows: — 



"The experiments of Castle on the amount of black in the coat 

 of hooded rats have been interpreted by their author to show that selection 

 on continuous variation within a strain can shift the mean of the variation- 

 curve. I am repeating these experiments, and as I have only bred souie 

 few hundreds T am not yet prepared to state how many genetic factors 

 can constitute the difference between a dark rat and a light one. But 

 I find, that selection has effect only in so far as one chooses between 

 individuals differing in genetic constitution, l)ut is without effect when 

 the choice is made between individuals with the same genetic factors, 

 but differing through the effect of non-genetic ones". 



I have awaited with some curiosity, but up to this time without 

 comment, some further account of Hagedoorns "few hundnnls" of rats 

 and their "genetic" and "non-genetic" factors. Spurred on by my silence 

 and mv continued adherence to the idea tliat selection is effective in 



