90 THE AMERICAN NATURALIST [Vol. L 



work on the selection problem is vastly superior to my 

 own. Since the subject of such comparison has been 

 opened it gives me great pleasure to pay tribute, in all 

 sincerity, to Professor Castle's splendid series of experi- 

 ments on selection in rats. In respect of the numbers of 

 animals involved and their superior adaptability for such 

 an experiment, his work with rats altogether transcends 

 anything which has been done with fowls. These selec- 

 tion experiments constitute an achievement of which their 

 author may well be proud. I have ventured to disagree 

 with Professor Castle's interpretation of the results for 

 reasons which will presently be stated. But this differ- 

 ence of opinion, I would most strongly emphasize, con- 

 cerns only the interpretation. We are at one in our high 

 admiration of the factual basis afforded by the rat experi- 

 ments. 



Ill 



Granting all this, however, it seems to me that possibly 

 the case against my studies of fecundity in toto is not quite 

 so bad as Castle makes it out to be. Let us examine his 

 points seriatim. In the first place the strictures upon the 

 character egg production on p. 714 seem to me to overdo 

 the matter a bit. It is of course true that it is a character 

 confined in its expression to one sex, though that it is also 

 a character which is transmitted by the other sex even 

 Castle somewhat grudgingly admits (p. 715). It also is a 

 character which comes to expression only in the adult. 

 Of this Castle makes a great point throughout his paper, 

 emphasizing that this means that only a small proportion 

 of all offspring born can take part in selection experi- 

 ments. From the standpoint of methodology this point 

 has nothing like the significance which Castle attributes 

 to it, for the very simple reason that in all breeding ex- 

 periments, his own included, there is a vast amount of 

 random sampling between the population of parental 

 genes and the population of offspring somata. When 

 Professor Castle breeds a pair of rats only a very few 



