xliv INTRODUCTION 



and of the extraordinary and specific influence which the 

 pituitary, thyroid, reproductive and other glands exert upon 

 remote parts of the body, and indeed of many other remark- 

 able correlations existing between apparently disconnected 

 parts, our empirical knowledge is surely far too slight to 

 offer any kind of firm basis for a large-reaching deduction 

 like that of Weismann.^ 



The advocates of use-inheritance have in all cases devoted 

 themselves to proving that it might be the true factor in 

 evolution : they have then assumed that it is the true 

 factor. Weismann equally has opposed them on the first 

 groimd, denying that it might be the true factor. From 

 this shifting and dubious morass of argumentation, we may 

 advisedly transfer our attention to the simple question of 

 fact and experience. And once on this solid ground we 

 find that not one single proved genuine instance of use-inheri- 

 tance has ever at any time been discovered. 



I have not forgotten, indeed, about the guinea-pigs of 

 Brown-Séquard, and am well acquainted with the nimierous 

 alleged facts brought forward by investigators of all kinds. 

 Not one of them but is susceptible of some other explanation. 

 It is difficult to deny that use-inheritance often appears the 

 easiest and most straightforward method : it is just that 

 very facihty of explanation which gives it such an enormous 

 hold on untrained minds. Yet the trained biologist will 

 attach not the shghtest importance to that straightforward 

 and plausible air, for he well knows that nature's methods 

 are rarely of the kind that a human being regards as simple 

 or straightforward. In short, all this is simply going back 

 to the tiresome question as to whether use-inheritance 

 might happen. We do not want the production of cases in 



* Since the above was printed, I have received advance proofs of Professor MacBride's 

 forthcoming work on the Embryology of the Invertebrates, through the courtesy of 

 Mr. Walter Heape, F.R.S., the general editor of a series of text-books of Embryology 

 shortly to be published. Professor MacBride suggests that the discovery of hormones 

 by Professor Starling may afford a clue as to a possible modus operandi of the inheritance 

 of acquired characters. He quotes Professor Langley to the effect that if an animal 

 changes its structure in response to a changed environment the hormones produced 

 by the altered organs will be changed : and these altered hormones circulate in the 

 blood and bathe the growing and maturing genital cells. 



