MECHANISM OF HEREDITY 15 



assume is that organisms transmit their struc 

 ture to their descendants, but in such a manner 

 as to permit of slight variations, on which 

 natural selection then acts in such a way that 

 the structure is, generation by generation, more 

 and more perfected and elaborated. With 

 this perfecting of the structure which makes 

 for the survival of the species there, of course, 

 goes hand in hand the elaboration of the 

 mechanism needed for securing the inheritance 

 of the more perfect structure. 



On the essential mechanism of hereditary 

 transmission, recent investigation, and par 

 ticularly the work of Weismann, has thrown 

 a flood of light. The germ-plasm, from which 

 parent and offspring are alike developed, is, 

 we have now reason to believe, passed on * 

 qualitatively unaltered, or almost unaltered, 

 from parent to offspring. It is constantly 

 increasing in amount by a simple process of 

 growth or quantitative increase; but as regards 

 chemical structure and composition it remains 

 the same. The offspring resembles the parent 

 for the simple reason that both originate from 

 material which is qualitatively identical, and 

 which is placed originally in qualitatively the 



