, 

 INHERITANCE OF ACQUIRED CHARACTERS 189 



cbemotaxis. In the case of Spirogyra, however, discussed in 

 Chapter X, 1 it certainly seems as if chemotaxis were not sufficient 

 to account for the phenomena. 



Belief in the possibility of the transmission of acquired 

 characters from somatic to germ cells by no means obliges us to 

 throw over Weismann's theory of determinants. Indeed it seems 

 necessary to postulate the existence in the germ plasm of some 

 such material priraordia as the responsible agents in the trans- 

 mission of heritable characters in order to account for the 

 Mendelian phenomena of hybridism, and especially the existence 

 of interchangeable unit characters, which will be dealt with in 

 the following chapter. Moreover, the theory of determinants, as 

 we have already seen, harmonizes very well with what we know 

 of the microscopic structure of the germ plasm and its behaviour 

 in cell-division and conjugation. 



It may be that it is the determinants themselves that are 

 influenced by stimuli received from the somatic cells. It is even 

 possible that each different kind of determinant is " tuned " 

 to respond to vibrations of a particular wave-length, emanating 

 from corresponding determinants in the nuclei of somatic cells of 

 a particular kind. Modifications of these somatic cells may then, 

 by altering the character of the vibrations in the determinants of 

 their own nuclei, affect the corresponding determinants in the 

 distant germ cells in a similar manner. By means of some such 

 hypothesis as this, which would be strictly in accordance with 

 modern physical ideas on the subject of the transmission of 

 electrical energy from one group of electrons to another at a dis- 

 tance, any a priori difficulty in accepting the possibility of the 

 inheritance of acquired characters might be removed. 



The case of neuter insects has frequently been adduced as a 

 serious stumbling block in the way of the theory of the origin of 

 permanent, heritable characters from somatogenic modifications, 

 for these neuters possess features of their own which are not 

 shared by the males and perfect females and which, as the 

 neuters do not themselves produce offspring, they cannot trans- 

 mit directly to future generations. According to Weismann's 

 theory these characters are supposed to result from fortuitous 

 favourable variations of the germ plasm of the parents, which are 

 accumulated and intensified under the influence of natural 



1 Pp. 142-3. I have perhaps laid too much stress upon this case ; chemotaxis 

 may have more to do with it than appears at first sight. 



