448 HEREDITY AND DEVELOPMENT 



to reach forward from this formulation to more precise observa- 

 tion and experiment. It goes without saying that the moment 

 the symbolic notation is shown to be inconsistent with demon- 

 strable facts, it must be thrown overboard and replaced by 

 another. 



2. It is difficult, Ziegler says, to think out clearly what we 

 mean by a unit-character and by its being represented by a 

 unit-germinal-constituent, whether pangen or determinant. 

 Many a quite definite character of an organism depends upon 

 a multitude of growth-conditions, and to conceive of the char, 

 acter being represented in the germ by one representative 

 particle is as difficult as it is to conceive of an infinite number 

 of representative particles, one for each item in the character. 



But it should be noted that Weismann simply assumes as 

 many determinants in the germ-plasm as there are parts in 

 the organism capable of independent and transmissible variation. 

 The fiddling string and bow on a grasshopper's thigh and wing 

 will have at least one determinant each, but one determinant 

 may suffice for all the millions of red blood corpuscles in man. 

 Again, Weismann expressly emphasises his view that " deter- 

 minants are not seed-grains of individual characters, but co- 

 determinants of the nature of the parts which they influence. 

 There are not special determinants of the size of a cell, others 

 of its specific histological differentiation, and still others of its 

 duration of life, power of multiplication, and so on ; there are 

 only determinants of the whole physiological nature of a cell, 

 on which all these and many other ' characters ' depend." Or 

 again, "There are no determinants of 'characters,' but only 

 of parts. The germ-plasm no more contains determinants of 

 a ' crooked nose ' than it does those of a butterfly's tailed wing ; 

 but it contains a number of determinants which so control 

 the whole cell-group in all its successive stages, leading on to 

 the development of the nose, that ultimately the crooked nose 

 must result, just as the butterfly's wing, with all its veins, mera- 



