6l6 THE HISTORY OF BIOLOGY 



example, the attempts of Little and Bagg" by passing Rontgen rays through 

 female rats to induce defects in the eyes and other parts of the body of their 

 offspring, and the experiments of Harrison^ with melanism in butterflies 

 induced by the introduction of metallic salts in the food. However, there 

 are no doubt obstinate anti-Lamarckists who have explained or will eventu- 

 ally explain even these results in a different way. In this connexion may 

 also be mentioned the recently published attempt of Professor Muller, of 

 Austin, Texas, to produce mutations in Drosophila by means of extreme 

 temperatures and Rontgen rays. 



The whole of this problem of evolution is of course highly involved 

 and its discussion must, as far as our own times are concerned, terminate 

 in a number of unanswered questions. First of all, selection; that it does 

 not operate in the form imagined by Darwin must certainly be taken as 

 proved, but does it exist at all? It is obvious that by the influence of external 

 conditions, especially such as interfere with sudden violence, a thinning-out 

 of the species is possible. If, for instance, a quantity of seed from a southern 

 climate is sown in a northern country, the delicate plants will die, whereas 

 the hardy ones will live, but this selection is only a matter of relation to 

 cold and proves nothing as to the quality of the individuals in other respects. 

 But the competition between the individuals, in which Haeckel thought he 

 saw true selection — does it exist at all, or is it only imaginary, as O. Hert- 

 wig affirmed? And outside influence — has it no effect whatsoever upon the 

 germinal plasm and offspring of the individuals, or is there really any such 

 influence in the form of some kind of mutational Lamarckism? 



These and many other questions it is for the future to answer. We have 

 now followed the history of biology up to our own times; our task is 

 fulfilled. 



"^ Little and Bagg, Anat. Record, Vol. XXIV, 1913. 



3 Proceedings of the Royal Society of London, ser. B, Vol. XCIX, 1516. 



