THEORIES OF WEISMANN AND DE VRIES 393 
tions and those of my fellow-workers, not because I regard 
the picture as incomplete or incapable of improvement, 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 
more 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 theory as a whole involves so many 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 confine 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: ‘‘(1) 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 conception of 
the germ-plasm. As is well known, animals and plants 
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 
