THE MODES OF REPRODUCTION 21 



are the structures of the germ-plasm which deter- 

 mine the characters of the adult organism, and it 

 will later be of great importance to inquire as to 

 the influences which any adult organism can bring 

 to bear upon the determinants of the reproductive 

 cells which it bears, and by which it is destined to 

 reproduce itself. But Weismann regards it as neces- 

 sary, and with justice, to assume that even these 

 determinants are not the ultimate living units. 

 These hypothetical constituents of each determinant 

 he calls biophores. They are the ultimate living 

 units. It is not inconceivable that they may be 

 identical in all living things. 



Now Weismann is by no means the first or only 

 biologist to postulate the existence of the specialised 

 living units which he calls determinants. They have 

 received at least a dozen difterent names from as 

 many biologists during the past forty years. But in 

 point of fact the originator of this conception was a 

 student who approached biology from the outside. 

 It is in Herbert Spencer's " Principles of Biology " 

 that this idea is first to be met, long before we had 

 attained to our present extended knowledge of the 

 reproductive process. Furthermore, the Spencerian 

 conception has gained little if at all from the efforts 

 of the many workers who have since adopted it. 

 Spencer saw that, on the one hand, the coll must 

 be regarded as the raorphological ^ unit of living 

 organisms. On the other hand, there must necessarily 

 be a chemical unit, consisting of the simplest com- 

 bination of molecules capable of displaying life. 



1 Morphology is the science of form in living things. We owe 

 the term to Goethe. 



