26 THE BIOLOGICAL PROBLEM OF TO-DA Y 



necessarily follow one another in a regular order, 

 and thus the thousands and hundreds of thousands 

 of hereditary parts are gradually formed, each in 

 its right place, and each provided with the proper 

 determinants. The construction of the whole body, 

 as well as its differentiation into parts, its segmenta- 

 tion, and the formation of its organs, and even the 

 size of these organs determined by the number of 

 cells composing them depend upon this com- 

 plicated disintegration of the determinants in the 

 id of germplasm. The transmission of characters 

 of the most general kind that is to say, those 

 which determine the structure of an animal as well 

 as those characterising the class, order, family, and 

 genus to which it belongs are due exclusively to 

 this process.' 



This mechanism of differentiating division fails 

 to explain the phenomena of reproduction and of 

 regeneration. For these Weisrnann has the follow- 

 ing ancillary suppositions : 



The first is the already-described hypothesis of 

 continuity of the germplasm. As the disintegration 

 of the germplasm into determinants, occurring in the 

 development of an egg into an organism, is a process 

 which cannot be retraced, and, as the future repro- 

 ductive cells of the organism must contain undisinte- 

 grated, perfect germplasm, it follows that the germ- 

 plasm in the germ-cells of the child must have come 

 directly from the original germplasm of the parent. 

 During the development, as Weismann assumes, only 

 a few of the ids, each of which contains all the 

 necessary germs, break up by differentiating division 



