328 THE EVOLUTION OF ANIMAL BEHAVIOUR 
animals that escape elimination are those in which the varia- 
tions are of such a nature as to conduce to this end. 
It will be seen that, on the hypothesis of organic heredity, 
thus briefly sketched, continuity can, in strictness and, as we 
may phrase it, in its first intent, only be predicated of the 
-germinal substance ; but that this substance gives rise to pro- 
ducts—active vigorous animals behaving in certain ways, each 
after his kind—which hold similar germinal substance in trust 
for future use. Natural selection deals with the trustees ; and 
if they succumb, that which they hold in trust is lost. To put 
the matter in another way : Nature says to the germinal sub- 
stance, “By your products you must be judged in accord- 
ance with the criterion of utility and efficiency.” Practical 
use in the give and take of active life is the touchstone of all 
behaviour which makes for survival. This being secured, there 
may be a balance of behaviour for other purposes. But in 
animals the balance is not of large amount, and other purposes 
have not taken form and direction. Jt should be clearly 
noticed that, on the hypothesis we are considering, use is 
the test of survival, and though it is not the direct cause 
of variations, it affords their sanction in survival. That 
animal escapes elimination whose behaviour is of practical use ; 
and it holds in trust for the future a store of germinal sub- 
stance from which is produced a successor capable of behaving 
in like manner. 
The whole drama of organic evolution may be regarded as 
the realization in a succession of individuals of the evolving 
potentiality of continuous lines of germinal substance. The 
successive individuals die—but the germinal substance lives 
on in their heirs, if they have any. In virtue of what inti- 
mate and hidden structure or disposition of parts the germ 
possesses this potentiality we do not know. The ovum of 
a dog is a microscopic speck less than one-hundredth of an 
inch in diameter ; the sperm is far more minute. They unite, 
and their nuclei coalesce. The cellular product divides and 
subdivides. The cell colony absorbs nutriment from the 
maternal tissues, Division proceeds apace, and the cells are 
