EVOLUTIONARY THEORIES SINCE DARWIN 237 
Darwin promulgated it, has dropped out of considera- 
tion almost entirely. DeVries of recent years has re- 
vised it, but with distinct modifications, and most bi- 
ologists pay no attention to it. 
There is a school of biologists, headed by Weiss- 
man, who have come to be known as Neo-Darwinians. 
These men have insisted that Natural Selection, if 
properly understood and developed, is quite sufficient 
to account for the fact of evolution, including the ap- 
pearance of variations. Weissman himself is a micro- 
scopist of more than common skill. He is thoroughly 
accomplished in the most modern methods of killing, 
fixing, staining, and mounting. This worker’s ac- 
quaintance with the intimate structure of the cell is 
probably as great as that of any other man in the 
world. Weissman asserts that he has seen inside the 
nucleus all the machinery necessary to explain how 
the father hands over his qualities to his children. He 
insists, equally strongly, that this process is such that 
no father can hand to his child any qualities which 
he himself did not have at least in potentiality at his 
birth. Everything the individual acquires during his 
lifetime is his own possession, which he may use and 
develop to the utmost extent, but it dies with him. 
His children, born after he possesses it, can no more 
inherit it than those born before. Weissman ex- 
pressed this in his famous statement that “There is 
