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 in a 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 hke the old 



