INHERITANCE OF ACQUIRED CHARACTERS 161 



are not acquired characters in the biological sense. Ac- 

 quired characters are modifications of the somatic cells 

 which are induced by environment, use or disuse, acci- 

 dents or any other influences acting upon the body-cells 

 in such a way as to change their normal development. 

 According to Weismann, if the modifications are the result 

 of the presence of determiners in the germ-plasm, then 

 they are not properly designated as acquired characters. 



151. Somatoplasm and germ-plasm. From the view- 

 point of the biologist, all organic beings which reproduce 

 sexually are differentiated into two very clearly defined 

 groups of cells : the somatic group, which includes all 

 the cells concerned in the processes of nutrition, includ- 

 ing digestion, absorption and assimilation; the nerve 

 cells and all other cells involved in the physiological 

 activities of the organized being, except the reproductive 

 cells. 



Distinct and apart from the soma- or body-cells are 

 the germ-cells, the function of which is to provide for 

 the reproduction of the species. Weismann was the 

 first to point out clearly the very sharp division between 

 the fundamental organization and function of these two 

 groups. The somatoplasm has its origin in the germ- 

 plasm, and the direction of its development is controlled 

 by the determiners in the germ-plasm, but the germ- 

 plasm is not influenced in any fundamental way by the 

 somatoplasm. The soma is to be regarded in the nature 

 of a habitat for the successful activities of the germ-cells. 

 In a sense, the somatoplasm has no more influence upon 

 the developing germ-cells harbored within the soma than 

 does the soil upon the trees which may develop from 

 the seeds planted on its surface. 



The germ-plasm is continuous. It is a part of the 



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