MATERIAL CAUSES OF HEREDITY. 199 
of the maternal organism, and, no less mysterious, that at 
the same time the essential qualities of the paternal 
organism are transferred to the offspring by means of the 
male sperm, which fructifies the egg-cell by means of a 
viscid substance in which minute thread-like cells or zoo- 
sperms move about. But as soon as we compare the con- 
nected stages of the different kinds of propagation, in which 
the produced organism separates itself more and more as a 
distinct growth from the parental individual, and more or 
less early enters upon its independent career; as soon as 
we consider, at the same time, that the growth and develop- 
ment of every higher organism only depends upon the 
increase of the cells composing it—that is, upon their 
simple propagation by division—it becomes quite evident 
that all these remarkable processes belong to one series. 
The life of every organic individual is nothing but a 
connected chain of very complicated material phenomena 
of motion. These motions must be considered as changes 
in the position and combination of the molecules, that is, 
of the smallest particles of animated matter (of atoms 
placed together in the most varied manner). The specifi, 
definite tendency of these orderly, continuous, and inherent 
motions of life depends, in every organism, upon the 
chemical mingling of the albuminous generative matter to 
which it owes its origin. In man, as in the case of the 
higher animals which propagate themselves in a sexual 
manner, the individual vital motion commences at the 
moment in which the egg-cell is fructified by the spermatic 
filaments of the seed, in which process both generative 
substances actually mix; and here the tendency of the 
vital motion is determined by the specific, or more 
