ORIGIN: OF LIFE. 73 
‘undergo a direct process of development, we first 
begin to obtain such regularly-recurring and definite 
assemblages of animal and vegetal forms as are 
usually grouped under the name of ‘species.’ 
Until such assemblages of repeating individuals 
make their appearance—that is, until Homogenesis 
becomes the rule—the ‘laws of Heredity’ can 
scarcely be said to come into operation. Hence, the 
complexly-interrelated individuals constituting this 
vast underlying plexus of Infusorial and Cryptogamic 
life must remain wholly uninfluenced, so far as their 
form and structure are concerned, by what Mr. Darwin 
has termed ‘Natural Selection.’ Such vegetal and 
animal organisms, however, gradually tend to become 
more and more complex. An ascending develop- 
ment takes place; and as this occurs, the causes 
which originally sufficed to determine their form and 
structure, and which for a time continue to induce 
comparatively rapid and marked deviations, become 
less and less capable of bringing about structural 
modifications during the life of the individual. 
Changes which are now less rapidly accomplished 
have to be perfected in a succession of individuals. 
Thus is the operation initiated of those subtle and 
more slowly modifying agencies which have been 
so admirably illustrated by Mr. Darwin. 
But amongst. specific forms of slight complexity 
