EXTEJN^SIO^^S OF DAKWINISM 293 



factor, it would seiTe to account for the inordinate growth of cer- 

 tain structures, such as the exuberance of some secondary sexual 

 characters, and for the existence of determinate variations, that is 

 to say, variations along special or particular lines of adaptation." 



It may be well to give here Weismann's own definition of 

 what he means by " determinants," as quoted by Professor J. 

 Arthur Thomson in his fine volume on Heredity (p. 435) : 



" ' I assume,' Weismann says, ^ that the germ-plasm consists of 

 a large number of different parts, each of which stands in a definite 

 relation to particular cells or kinds of cells in the organism to be 

 developed — that is, tliey are * primary constituents' in the sense 

 that their co-operation in the production of a particular part of the 

 organism is indispensable, the part being determined both as to its 

 existence and its nature by the predestined particles of the germ- 

 plasm. I therefore call these Determinants, and the parts of the 

 complete organism which they determine Determinates," ^ 



Professor Thomson continues thus: 



" But how many determinants are to be postulated in any given 

 case? "Weismann supposes that every independently variable and 

 independently heritable character is represented in the germ-plasm 

 by a determinant. A lock of white hair among the dark may re- 

 appear at the same place for several generations; it is difficult to 

 interpret such facts of particular inheritance except on the theory 

 that the germ -plasm is built up of a large number of different de- 

 terminants. It may be pointed out that almost all biologists who 

 have tried to form a conception of the ultimate structure of living 

 matter have been led to the assumption — expressed in very varied 

 phraseology — of ultimate protoplasmic units which have the power 

 of growth and division. It is in no way peculiar to Weismann to 

 imagine biophors and to credit them with the powers of growing 

 and dividing.'' 



I quote these passages because Professor Thomson is thor- 

 oughly acquainted, not only with all Weismann's work, having 

 himself translated some of them, but also with that of other 



1 The Evolution Theory, 1004. vol. i. p. 355. 



