826 THE AMERICAN NATURALIST: [VOL XXXII. 
tion where development ends, and variation, the first step in 
evolution, begins. Whereas, in fact, it is difficult even to 
imagine how the closest possible scrutiny of the growing indi- 
vidual could detect the place where normal development ends 
and variation begins. 
Variation, in any concrete case, is simply the development 
of the individual in some different way, or to a degree beyond 
the attainment of its parents; but it is, nevertheless, normal 
constructive development. The whole secret of individual 
development lies in the fact that in the reproduction of grow- 
ing cells, the daughter cells are slightly different from the 
parent cells, greater uniformity occurring in each mass of the 
same tissue or organ, but absolute uniformity nowhere. The 
multiplication of similar cells in growth, and their gradual 
modification in the construction of dissimilar tissues and organs 
in development, are phenomena no less diverse than is the 
hereditary process of reproduction of individuals from the 
variational production of specific differences. Variation is 
exhibited whenever an organic body produces another body 
dissimilar to itself, whether that body be a cell or an individual. 
Heredity is exhibited in both cases in the phenomenon of 
reproducing that which has already appeared. 
Thirdly : Let us take another view of the subject and note 
the relation which variation and heredity bear to experience. 
In any concrete case of a growing organism the construction 
of a character according to heredity implies the experience of 
having previously constructed such a character, on the part 
of the parent, which is conceived of as the controlling cause of 
the process. Variation, on the other hand, is, when it first 
occurs, spontaneous, in so far as that means previous to experi- 
ence. So far as the individual, or the race to which it belongs, 
is concerned, the varying act is an original act; it does not 
depend upon specific experience. Heredity is, therefore, of 
the nature of habit or memory, and implies experience. Varia- 
tion is, in its intrinsic nature, original and genetic. 
Selection is one of the steps in the acquirement of heredity, 
and thus the “origin of species” by natural selection is the 
acquiring of a regular, or hereditary, method of development 
