194 GEOEGB JOHN EOMANES issi- 



begin by furnishing the explanation of what was 

 meant by the passage in the ' Contemporary Eeview ' 

 to which you alluded. 



I quite agree that Weismann's suggestion about 

 causes of variability is an admirable one. But it has 

 always seemed to me that it is comprised under 

 Darwin's general category of causes internal to the 

 organism (or, in his terminology, causes due to ' the 

 nature of the organism '). But besides this, he recog- 

 nised the category of causes external to the organism 

 (or the so-called Lamarckian principles of direct 

 action of environment, plus inherited efforts of use 

 and disuse). Now, anyone who accepts this latter 

 category as comprising verca causce, obviously has a 

 larger area of causahty on which to draw for his 

 theoretical explanations of variabiHty, than has a 

 man who expressly limits the possibility of such 

 causes to the former category. This is all that I 

 had in my mind when writing the line in the ' Con- 

 temporary Eeview ' which led you to suppose that I 

 was expounding W. without having read him; and 

 although I freely allow that the meaning was one 

 that required explanation to bring out, you may 

 remember that this meaning had nothing whatever 

 to do with the subject which I was expoundings 

 and therefore it was that I neglected to draw it out. 

 You will observe that, so far as the present matter 

 is concerned, it does not signify what Adews we 

 severally take touching the validity of Lamarckian 

 hypotheses. The point is, that anyone who sees 

 his way to entertaining them thereby furnishes 

 himself with a larger field of causality for explaining 



