1893. BIOLOGICAL THEORIES. 197 
This would seem to be obvious enough, and there would appear 
to be no need for any argument to establish the view here put 
forward, viz.:—that the ontogeny is not an epitome of the phylogeny, 
is not even a modified or ‘ falsified” epitome, is not a record, either 
perfect or imperfect, of past history, is not a recapitulation of the 
course of evolution. My excuse for urging what appears to me to be 
an obvious fact, is the existence of a statement the direct opposite of 
this view in almost every zoological text-book which has been pub- 
lished within the last fifteen or twenty years, as well as the frequent 
urging of the recapitulation theory in our colleges and universities, 
in the University Extension Lectures, and ina recent lecture given to 
the British Association, and even in the presidential address of one 
of our most eminent embryologists to the Biological Section of that 
Association. 
Incidentally, it may be well to point out the restricted sense in 
which I use the word “ variation.” To vary, is, I believe, to change 
or to become unlike, whatever the thing varying was previously like. To 
be unlike is to differ; not to vary. The unlikeness observable among the 
members of a species is variety, or difference, or unlikeness, but it is 
not variation. Variation is change in the average constitution of 
successive generations of a species leading to the production of a 
new species, or race, from an old one. I have myself used the term 
in another sense in a previous paper in this series, but that is no 
reason why I should continue to use it in a sense which is liable 
to lead, and indeed has led, to confusion. 
The terms “‘ vary’ and ‘ differ’? as above defined are not even 
partially synonymous. Difference and variation are respectively 
statical and dynamical (if I may use that term to express the opposite 
of statical). 
In order that any structure of the adult which varies, and hence 
ceases to exist as an adult structure at all, may become an ontogenetic 
record of that adult structure, it is necessary that variation should 
occur in a way utterly unlike the way in which it does actually occur. 
The more the adult structure comes to be unlike the adult structure 
of the ancestors, the more do the late stages of development undergo 
a modification of the same kind. This is not mere dogma, but is a 
simple paraphrase of Von Baer’s law. It is proved true, not only by 
the observations of Von Baer and of Darwin, already referred to, but 
by the direct observation of everyone who takes the trouble to com- 
pare the embryos of any two vertebrates, provided only he will be 
content to see what actually lies before him, and not the phantasms 
which the recapitulation theory may have printed on his imagination. 
In order to produce a “‘ record ”’ it is necessary that new chapters 
be added at the end of the pre-existing record. It is necessary, in 
fact, that as the adult structure varies in one direction, the late stages 
of development shall vary in another, so as to become, not more like 
the new adult structure than they were before, but more like the old 
