Growth Variations 179 
course of the life-history, though it is difficult to see how this 
has occurred. It is much more likely, if we may judge from 
available evidence, that every stage has had its counterpart in the 
ancestral form from which it has been derived by descent with 
modification. Just as the adult phase of the living form differs, 
owing to evolutionary modification, from the adult phase of the 
ancestor from which it has proceeded, so each larval phase will differ 
for the same reason from the corresponding larval phase in the life- 
history of the ancestor. Inasmuch as the organism is variable at 
every stage of its independent existence and is exposed to the action 
of natural selection there is no reason why it should escape modifica- 
tion at any stage. 
If there is any truth in these considerations it would seem to 
follow that at the dawn of life the life-cycle must have been, either 
in posse or in esse, at least as long as it is at the present time, and 
that the peculiarity of passing through a series of stages in which new 
characters are successively evolved is a primordial quality of living 
matter. 
Before leaving this part of the subject, it is necessary to touch 
upon another aspect of it. What are these variations in structure 
which succeed one another in the life-history of an organism? Iam 
conscious that I am here on the threshold of a chamber which 
contains the clue to some of our difficulties, and that I cannot enter 
it. Looked at from one point of view they belong to the class of 
genetic variations, which depend upon the structure or constitution 
of the protoplasm; but instead of appearing in different zygotes’, 
they are present in the same zygote though at different times in its 
life-history. They are of the same order as the mutational variations 
of the modern biologist upon which the appearance of a new character 
depends. What is a genetic or mutational variation? It is a genetic 
character which was not present in either of the parents. But these 
“growth variations” were present in the parents, and in this they 
differ from mutational variations. But what are genetic characters ? 
They are characters which must appear if any development occurs. 
They are usually contrasted with “acquired characters,” using the 
expression “acquired character” in the Lamarckian sense. But 
strictly speaking they are acquired characters, for the zygote at first 
has none of the characters which it subsequently acquires, but only 
the power of acquiring them in response to the action of the environ- 
ment. But the characters so acquired are not what we technically 
understand and what Lamarck meant by “acquired characters.” 
They are genetic characters, as defined above. What then are 
1 A zygote is a fertilised ovum, i.e. a new organism resulting from the fusion of an 
ovum and a spermatozoon. 
12—2 
