THEORIES OF WEISMANN AND DE VRIES 395 
the same stuff. The rise of the idea of germinal continuity 
has been indicated in Chapter XIV’, where it was pointed out 
that Weismann was not the originator of the idea, but he is nev- 
ertheless the one who has developed it the most extensively. 
Complexity of the Germ-Plasm.—The gcrm-plasm has 
been molded for so many centuries by external circum- 
stances that it has acquired an organization of great com- 
plexity. This appears from the following considerations: 
Protoplasm is impressionable; in fact, its most characteristic 
feature is that it responds to stimulation and modifies itself 
accordingly. These subtle changes occurring within the 
protoplasm affect its organization, and in the long run it is 
the summation of experiences that determines what the pro- 
toplasm shall be and how it will behave in development. 
Two masses of protoplasm differ in capabilities and poten- 
tialities according to the experiences through which they have 
passed, and no two will be absoluiely identical. All the time 
the body was being evolved the protoplasm of the germinal 
elements was being molded and changed, and these ele- 
ments therefore possess an inherited orgnization of great 
complexity. 
When the body is built anew from the germinal ele- 
ments, the derived qualities come into play, and the whole 
process is a succession of responses to stimulation. This is 
in a sense, on the part of the protoplasm, a repeating of its 
historical experience. In building the organism it does not 
go over the ground for the first time, but repeats the activities 
which it took centuries to acquire. 
The evident complexity of the germ-plasm made it 
necessary for Weismann, in attempting to explain inheritance 
in detail, to assume the existence of distinct vital units within 
the protoplasm of the germinal elements. He has invented 
names for these particular units as biophors, the elementary 
vital units, and their combination into determinants, the 
