PRESIDENTIAL ADDRESS. 267 



be overlooked that certain rather strongly marked variations 

 • . . frequently recur, owing to a similar organization 

 being similarly acted on, — of which fact numerous instances 

 could be given with our domestic productions. . . . 

 There can also be little doubt that the tendency to vary in 

 the same manner has often been so strong that all the 

 individuals of the same species have been similarly modified 

 without the aid of any form of selection" {Origin of Species^ 

 p. 72). Now in the case of our flat-fishes' eyes the similar 

 modification of considerable numbers of individuals (which 

 would seem to be a sine qud non on the hypothesis of gradual 

 transformation) may be either due to laws of organization 

 or to the inherited effects of use. A twisted skull and 

 asymmetry of eyes seems a priori unlikely as the outcome 

 of any inherent organic tendency, even though it were, as 

 is possible, correlated with the concomitant tendency to lie 

 on the side. 



The inherited effects of use and disease would in this, and 

 a great number of other cases, convenient^ account for a 

 large number of individuals varying in exactly the required 

 direction. But this in itself does not justify us in accepting 

 this view of the matter, unless it can be conclusively shown 

 that all other explanations are barred by their improbability. 

 The consideration of this case, however, suggests a possible 

 line of experimental observation. Would it not be possible, 

 without in any way maiming or giving pain, to induce in 

 domesticated animals or birds, by weighting or handicapping 

 one side of the body, a lop-sided development? If this were 

 continued through a series of generations, without any 

 selection, it might then be seen whether there was any 

 tendency for this lopsidedness to be inherited. High action 

 in the horse can be induced by weighting the limbs. I am 

 not aware whether this has been done for a series of genera- 



