WEISMANN'S CONCESSIONS. 18 1 



" The origin of a variation is equally independent of selection 

 and of amphimixis, and is due to the constant recurrence of slight 

 inequalities of nutrition in the germ-plasm which affect every 

 determinant in one way or another, and differ even in the same 

 germ-plasm not only in different individuals but also in different 

 regions. These variations are at first infinitesimal, but may ac- 

 cumulate ; and, in fact, they must do so when the modified condi- 

 tions of nutrition which gave rise to them have lasted for several 

 generations. In this way deviations may occur in the structure 

 of single determinants or of groups of them never, perhaps, in 

 all ids at once, but at any rate in several or even many of them. 

 A doubling of certain determinants of the germ-plasm may origi- 

 nate in the same way. The process of amphimixis has an impor- 

 tant share in the accumulation of these modified determinants, for 

 it may raise the minority previously existing in the two parents 

 to a majority by combining their halved germ-plasms. Then, and 

 then only, does selection begin to take place." * 



After all this it is certainly surprising that he should still 

 cling to his former declaration that acquired characters are not 

 transmissible. After abandoning all his premises he still adheres 

 to his conclusion. Dr. J. G. Romanes, who has been one of his 

 most liberal critics, after characterizing the latter part of the 

 Germ-Plasm as " a right-about-face manoeuvre/' says that his first 

 impulse " was to cancel all the criticisms which I had written of 

 the Weismannian theory/' f and it really seems as though it were 

 time to drop this prolonged discussion. Its further continuance 

 must certainly be chargeable to his own course as pursued in 

 Chapter XIII of his Germ-Plasm, and in his reply to Mr. Spencer 

 in the face of these concessions. It is somewhat difficult to under- 

 stand how he is able to reconcile these apparently conflicting 

 views. That he does not limit the influence of external conditions 

 to the germ-plasm proper, or fertilized germ cell, is apparent from 

 his cheerful acceptance of Nageli's " opinion that all variations 

 are slowly prepared in the idioplasm in the course of generations 

 before they become apparent," and we must suppose him to admit 

 that it is the hereditary units themselves that are undergoing 

 these transformations. In my address before the Biological Soci- 

 ety I had referred to this in the following language : 



" You will understand that I am speaking of variations which 

 take place in the germ cells and sperm cells of parental organisms 

 before they blend in the fertilized ovum. Most of Weismann's 

 argument is directed to show that the fertilized ovum itself can 

 not be affected by any transforming influence acting upon the 



* The Germ-Plasm, p. 431. 



f The Open Court, vol. vii. Chicago, September 14, 1893. Supplement, p. iii. 



