290 THE WHENOE AND THE WHITHER OF MAN 



calling in question the all-sufSciency of natural selec- 

 tion and tlie modifying power of environment, and by 

 emphasizing, probably overmuch, the importance of 

 initial inherent tendency, whose value has been en- 

 tirely neglected by many evolutionists. 



Lack of space compels us to leave unnoticed most of 

 the exceedingly valuable suggestions of Nageli's brill- 

 iant work. 



It is still less possible to do any justice in a few 

 words to Weismann's theory. Into its various modi- 

 fications, as it has grown from year to year, we have 

 no time to enter. And we must confine ourselves to 

 his views of variation and heredity. 



In studying protozoa we noticed that they repro- 

 duced by fission, each adult individual dividing into 

 two yormg ones. There is therefore no old parent left 

 to die. Natural death does not occur here, only death 

 by violence or unfavorable conditions. The protozoa 

 are immortal, not in the sense of the endless persist- 

 ence of the individual, but of the absence of death. 

 Heredity is here easily comprehensible, for one-half, or 

 less frequently a smaller fraction, of the substance of 

 the parent goes to form the new individual. There is 

 direct continuity of substance from generation to gen- 

 eration. 



But in volvox a change has taken place. The fer- 

 tilized egg-cell, formed by the union of egg and sper- 

 matozoon, is a single cell, like the individual result- 

 ing from the conjugation or fusion of two protozoa. 

 But in the many-celled individual, which develops out 

 of the fertilized egg, there are two kinds of cells. 1. 

 There are other egg-cells, like the first, each one of 

 which can, under favorable conditions, develop into a 



