THEORIES OF WEISMANN AND DE VRIES 393 



tions and those of my fellow-workers, not because T regard 

 the picture as incomplete or incapable of imjjrovement, but 

 because I believe its essential features to be correct, and 

 because an eye-trouble which has hindered my work for 

 many years makes it uncertain whether I shall have much 

 miore time and strength granted to me for its further elabora- 

 tion." 



The germ-plasm theory is primarily a theory of heredity, 

 and only when connected with other considerations does it 

 become the full-fledged theory of evolution known as Weis- 

 mannism. The theorv as a whole involves so manv intricate 

 details that it is difficult to make a clear statement of it for 

 general readers. If in considering the theories of Lamarck 

 and Darwin it was found advantageous to conline attention 

 to salient points and to omit details, it is all the more essential 

 to do so in the discussion of Weismann's theory. 



In his prefatory note to the English edition of The 

 Evolution Theory Thomson, the translator, summarizes Weis- 

 mann's especial contributions as: " (i) the illumination of the 

 evolution process with a wealth of fresh illustrations; (2) 

 the vindication of the ^germ-plasm' concept as a valuable 

 working hypothesis; (3) the final abandonment of any 

 assumption of transmissible acquired characters; (4) a 

 further analysis of the nature and origin of variations; and 

 (5), above all, an extension of the selection principle of 

 Darwin and Wallace, which finds its logical outcome in the 

 suggestive theory of germinal selection." 



Continuity of the Germ-Plasm. — Weismann's theory is 

 designated that of continuity of the germ-plasm, and in con- 

 sidering it we must first give attention to his conce])tion of 

 the germ-plasm. As is well known, animals and })lants 

 spring from germinal elements of microscopic size; these are, 

 in plants, the spores, the seeds, and their fertilizing agents; 

 and, in animals, the eggs and the sperms. Now, since all 



