THE PRESIDENTIAL ADDRESS 19 



the same result, but even so, he believed the future would prove 

 that physicists were mistaken and that the atom was far smaller. 



It is impossible to say more than a few words about the very 

 interesting and important discussion on ' The present state of the 

 Theory of Natural Selection ' held at the Royal Society on May 14 

 last year. The subject was approached from many points of view 

 by both zoologists and botanists, and their conclusions were very 

 welcome to Darwinians who remembered the earlier opinions 

 expressed when Mendel's great work was rediscovered. I think, 

 however, that Prof. D. M. S. Watson, in the opening address, was 

 inclined to underestimate the value of the existing evidence for a 

 * selective death rate,' although everyone will agree that ' any new 

 evidence ... or indeed any suggestion of cases which might be 

 capable of investigation,' would be most desirable. 



I may briefly mention a few experiments brought before Section D 

 at the Bristol meeting in 1898 beginning with the work of Weldon 

 and Thompson on the Common Shore Crab, showing that the 

 effect of china clay and other impurities in the sea at Plymouth was 

 selective and promoted changes of shape which ensured that the 

 water flowing over the respiratory surface was more efficiently 

 filtered. 



Then, on the subject of chance, the heroic help rendered by Mrs. 

 Weldon, who four times recorded the result of 4,096 throws of dice, 

 showing that the faces with more than three points were on the 

 average, uppermost slightly more often than was to be expected. 

 It comes back to me very clearly because of the interesting explana- 

 tion — that the points on dice are marked by little holes scooped out 

 of the faces, and that points 6, 5, and 4, respectively opposite 1,2, 

 and 3 are somewhat lighter, more of the ivory having been removed ; 

 also because of Francis Galton's delight and his humorously 

 expressed wonder whether the facts had been realised by those 

 who had an interest other than scientific in the throwing of dice. 



Experimental evidence was also submitted by Miss Cora B. 

 Sanders (Mrs. C. B. S. Hodson) and myself, proving that when the 

 rough, angular pupa of the small tortoiseshell butterfly ' is sus- 

 pended from a surface against which it stands out conspicuously, 

 it is in far greater danger than when it is fixed to one upon which it 

 is concealed.' 



To the observer of living creatures, however, the most convincing 

 evidence is provided by animals themselves. When a wild bird is 

 seen to capture some conspicuous butterfly or moth and then 

 immediately to reject it the association between inedibility and a 

 warning colour is more convincingly suggested than when insects 

 are offered to animals in confinement, although such experiments 



