CONTINUITY IN EVOLUTION 325 
why a certain compound of oxygen and hydrogen in certain 
proportions has the properties of that which we call water ? 
Let us note the distinction between saying, as we said 
above, that life is the behaviour of protoplasm, and asserting 
that life is the cause of this behaviour. The one is a scientific 
statement of observed fact, the other an explanation of the 
fact in metaphysical terms, a reference of the fact to its under- 
lying cause. So long as we quite clearly understand that we 
are talking the language of metaphysics, we may speak of life 
as a cause of organic behaviour; but let us be careful to 
remember that the statement has no more value for science 
than the assertion that aqueosity is the cause of the behaviour 
of water. 
Leaving on one side, then, the natural origin of protoplasm, 
the conditions of whicn are unknown, we find that, as a matter 
of observation, every bit of living substance, the history of 
which has been traced, is a fragment detached from some other 
bit which behaved in the same way. This is the basal fact of 
the continuity of organic evolution. But such a detached 
fragment has the property of increasing by taking up from 
the environment more of those elementary materials from 
which it is itself compounded in subtle synthesis. Nay, 
further, every fragment of which we know the history is found 
to increase in such a way as to reach, in form, structure, and 
idiosyneracies of behaviour, the likeness of the organism— 
plant or animal—from which it was derived. In the higher 
plants and animals the separated fragments or cells are the 
ova and sperms, or their equivalents, which unite, with fusion 
or coalescence of their nuclear matter, and thus give rise to a 
new individual in the course of embryological development. 
Now, as we have already seen, much modern biological dis- 
cussion centres round the question whether the detached repro- 
ductive fragment, ovum or sperm as the case may be, is derived 
from the whole body of the parent, by what Darwin termed 
pangenesis or in some other way, or only from germinal sub- 
stance set apart in development for this end. And we have 
provisionally accepted the hypothesis that it is the direct 
