272 THE WORLD OF LIFE CHAP. 



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, they 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} " l 



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 

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

 interpret such facts of particulate inheritance except on the theory 

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

 determinants. 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 

 thoroughly acquainted, not only with all Weismann's works, 

 having himself translated some of them, but also with the 

 work of other European and American writers on this very 

 difficult problem ; and he arrives at the conclusion, that 

 Weismann's theory is the most carefully and logically 

 worked out, and that some such conception is essential for 

 a comprehension of the wonderfully complex phenomena of 

 heredity. He also quite agrees with the conception that as 

 these vital elements of the germ-plasm grow and multiply 

 during the life of the organism, they must be nourished 

 by fluids derived from it, and that there must be slight 

 differences between them in size and vigour, and a struggle 

 for existence in which the most vigorous survive. These 

 1 The Evolution Theory, 1904, vol. i. p. 355. 



