CHARACTERS IN HEREDITY 159 



and the like, have, however, been shown to Men- 

 dehze, and further study will undoubtedly reveal 

 the existence of additional unit characters. We 

 should also bear in mind that we have no means 

 of identifying unit characters except as they drop 

 out of existence in certain individuals. Many 

 unit characters are probably of such vital impor- 

 tance to the organism that they cannot be dis- 

 pensed with, for when they are lost the organism 

 ceases to exist. In such cases the existence of 

 unit characters, however probable, can not be 

 unmistakably demonstrated by any method now 

 known to us. Fragmentary as our present 

 knowledge is, it is doubtful whether any category 

 of organs, quantities, or parts can be mentioned 

 which is not subject to Mendelian inheritance. 

 If we could only discover some means of sup- 

 pressing particular unit characters, what an in- 

 strument for unraveUng the mysteries of inheri- 

 tance would be ours ! 



Time does not suffice to discuss the mutability 

 or immutabihty of the unit characters, the pos- 

 sibility of new characters arising de novo, and 

 other interesting but disputed questions. These 

 are matters with which the second fifty years 

 after Darwin will have to deal. 



