296 DARWINISM AND THE PROBLEMS OF LIFE 



and generally in a few of the further, cleavages of the 

 ovum the halves of all the rudimentary parts pass into 

 each daughter-cell, and they complete each other, so 

 that the first segmentation-cells have still the power of 

 constructing the whole organism, because they have the 

 rudiments of all the organs. But in the further course 

 of development the rudimentary parts, which have not 

 yet made any use of their power to form organs, enter 

 into action. When the number of cells is large, the 

 dividing cells receive all the rudimentary parts, but 

 these do not remain united in the nucleus of the new 

 cells ; some of them pass into the protoplasm of the 

 cells, and thus give a definite character to them. When, 

 for instance, the development has proceeded far enough 

 for the construction of the alimentary canal to have 

 begun, the alimentary basic parts pass out of the 

 nuclei and give the new cells the character of alimen- 

 tary cells. The cells that afterwards separate from 

 these are, therefore, devoid of the alimentary parts. 

 As they divide further, the other bases of the various 

 organs pass out of their nuclei ; the nerve-parts convert 

 certain cleavage-cells into neural cells, and so on. In a 

 word, the basic or rudimentary parts continue to work 

 until the construction of the organism is completed. 

 Naturally, this description of the process does not rest 

 on observation, but is a theory, founded by Weismann ; 

 but it must be admitted that it makes the embryonic 

 development intelligible.^ 



This continuous transfer of the basic parts does not 



•^ The above is an outline of Weismann's " germ-plasm theory," the 

 most elaborate theory of heredity that we have. 



