I] THEORIES OF HEREDITY 139 



Weismann was led by his work on the origin of the 

 germ-cells to a belief in germinal continuity as 

 explained above, but the facts of regeneration of 

 lost parts and other related phenomena caused him 

 to give up the idea that a sharp distinction could be 

 drawn between the cells of the body and the germ, 

 and to substitute for it the idea of a distinction 

 between body-substance and germ-substance, or as 

 he calls it, body-plasm and germ-plasm. According 

 to this hypothesis, the egg contains germ-plasm 

 derived from that of the parent, and as the egg 

 develops the germ-plasm increases and becomes 

 distributed among the cells, and gradually, as the 

 cells become specialised to form the different parts, 

 the germ-plasm becomes converted into body-plasm 

 and builds up the varied kinds of cells of the 

 body. But some cells continue to possess the full 

 complement of ancestral germ-plasm, and these will 

 go to form the germ-cells of the next generation. 

 When an organ remains capable of regenerating 

 lost parts, it is assumed that germ-plasm having 

 the power to develop such parts remains in the cells 

 and becomes active when required. Germ-plasm can 

 thus be converted into body-plasm, but body-plasm 

 cannot become germ-plasm, and hence Weismann 

 assumes that no change brought about in the body 

 (by environment, etc.) but not affecting the germ-cells, 

 can be inherited by subsequent generations. It is 



