132 DARWINISM TO-DAY. 



is, that natural selection alone is capable of explaining all the 

 phenomena and facts of species-forming and descent. At 

 the same time he developed and announced the theory of the 

 continuity of the germ-plasm, 2 which, in a word, is the 

 theory of an absolute separation of the germ-plasm from 

 the soma-plasm and consequently the thorough independ- 

 ence of this germ-plasm from all influence and control of 

 the soma-plasm, i. e., all that part of the body other than 

 the germ cells. This carried with it the assumption that 

 all the phenomena of heredity and variation depended solely 

 on the germ-plasm and that the germ-plasm of any individual 

 is derived, unmodified by any somatic influences, directly 

 from the germ-plasm of its ancestors. This assumption in 

 turn led to the logical but startling conclusion that all the 

 capacity or possibility of variation for all time was present 

 in that primitive ancestral germ-plasm from which the germ- 

 plasm of all many-celled animals has been derived. But such 

 a nearly infinite capacity for furnishing variations demanded 

 the postulation of an equally nearly infinite capacity for ac- 

 tual physical or structural complexity on the part of the germ- 

 plasm itself, for biologists insist on a physical mechanism for 

 all the physiological phenomena they find in life. So Weis- 

 mann assumed an interesting but invisible and apparently 

 non-testable composition of germ-plasm out of life-units, 

 called biophors, grouped into particles of a second order called 

 determinants. The biophors are taken to be much larger 

 and more complex units than chemical atoms, or even than 

 molecules. They are groups of several to many molecules, 

 each biophor, however, still ultra-microscopic, and represent- 

 ing a single characteristic of cell-life. Each biophor is as- 

 sumed to possess the essential attributes of living substance, 

 viz., the capacity to assimilate food, to grow, and to repro- 

 duce itself. The groups of biophors called determinants 

 are larger, of course, but yet invisible to oUr best micro- 

 scopes, and each represents all the characteristics which a 



