96 THE CELL IN RELATION TO 



The first has been accepted by many acute bio- 

 logical thinkers as almost a logical necessity, and 

 has been developed, especially by Weismann, into 

 one of the most ingenious and elaborate specula- 

 tive constructions to be found in the whole his- 

 tory of biology. Its logical grounds need not 

 here be analyzed. I will only emphasize the fact 

 that the conception did not grow out of actual 

 studies on the cell, but was an imaginative con- 

 struction, based on the facts of variation and 

 heredity. It may be true ; but for the present we 

 i can only regard it as a kind of symbohsm, anal- 

 : ogous in some respects to the molecular-atomic 

 : symbolism of physical science, but of far more 

 doubtful validity. Those who find such a sym- 

 bolism useful will encounter no positive obstacle 

 in the known cytological facts — they may even 

 find in them a certain amount of indirect support 

 — but the assumption remains unverified, and is 

 probably unverifiable. 



The second postulate of pangenesis is wholly 

 unsupported by either experimental or cytolog- 

 ical evidence. There is not a particle of evidence 

 to show that in the higher forms of hfe cells pro- 

 duce gemmules or that the germ-cells are built 

 up by the aggregation of such bodies derived 

 from the somatic cells. The most fundamental 

 il contribution of cell-research to the theory of he- 

 redity is the law of genetic continuity by cell- 

 division. Cells arise only by the division of pre- 

 existing cells. And the stream of growth and 



