THE INDIVIDUAL AND THE SPECIES 185 



would be required for this purpose, and it must be 

 a mechanism involving only known chemical and 

 physical factors. It is safe to say that absolutely no 

 hint as to the nature of this mechanism is contained 

 in the hypothesis. 



The determinants must be able to grow by repro- 

 duction, or by the accretion of new biophors, since in 

 each generation new germ-cells are formed. If we 

 say that they grow by reproduction in the sense that 

 an organism grows by reproduction, we beg the question 

 of their means of formation. Do they grow by the 

 addition of similar substances in the way that a crystal 

 grows ? If so, the molecules of which they are com- 

 posed must exist in the lymph stream bathing the 

 germ-cells that is, the biophors themselves must 

 already exist in this liquid, for if we suppose that the 

 biophors are able to divide and grow by making use 

 of the protein substances which we know are present 

 in the lymph stream, then we confer upon these bodies 

 all the properties of the fully developed organism. 

 If they are present in the blood, then the composition 

 of the latter must be one of inconceivable complexity, 

 since it must contain as many substances as there 

 are distinct tissues in the animal body. We know, of 

 course, that this is not the case. How, then, are the 

 biophors reproduced ? 



We must leave this field of unbridled speculation 

 (which cannot surely be " the most exact and rational- 

 istic part of biology.") What the study of the repro- 

 duction of the organism does show is that something 

 which we call the specific organisation is handed 

 down from parent to offspring, and that this some- 

 thing may possess a high degree of stability. No 

 apparent change of significance can be observed in 

 the very numerous generation of organisms (the 2000 





