324 
On the Fundamental Conceptions of Biologij 
repeatedly said that I mean by the Principle of Homotyposis, "a numerical 
appreciation of the likeness and diversity among homotypes," and again, "the 
quantitative measurement of the degree of resemblance between undifferentiated- 
like organs being, so far as I am avk'are, a quite novel branch of investigation, I 
venture, with some hesitation, to introduce certain terms." Notwithstanding this 
definite statement as to what I mean by homotyposis Mr Bateson tells me that he 
should welcome my paper as an attempt — the only one so far as he knows — to 
emphasise and develop a conception introduced by him, namely, that " the 
resemblance whicli we call heredity may he a special case of the phenomenon, of 
symmetry" (p. 194). "The principle that Professor Pearson calls 'homotyposis' 
I have expressed by the statement that the variations of parts repeated in series 
may be ' similar and simultaneous.' Beyond this we cannot yet go. Professor 
Peai'son's statement of the principle fails to recognise one of the most important 
features of homotyposis. Expressed in my own terms, Professor Pearson's 
' homotyposis ' is the principle of ' similar and simultaneous variation ' restricted 
to undifferentiated like parts" (p. 201). 
Frankly I have not the least idea of what this " principle of symmetry " may 
be, or how "symmetry" on p. 194 is the same as "similar and simultaneous 
variation" on p. 201. I suppose they are definite biological conceptions, but to my 
purely mathematical mind both "symmetry" and "similarity" in this sense convey 
no meaning at all. As according to Mr Bateson " it would be easy to suggest 
terms better adapted to the expression of these conceptions " I heartily wish he 
had done so. My confusion, however, only becomes intensified when he tells us 
that he anticipates that " the largely analogous phenomena of rhythmical vibration 
will provide ready metaphors from which to construct a terminology" (p. 195, ftn.). 
I have had to consider largely symmetry, similarity and rhythmical vibration in 
the course of my stxidies, but how my mathematically concise notions on these 
points apply to, say, two leaves growing at different parts of a tree I am unable to 
appreciate. I venture to think that they are when applied without definition to 
vital phenomena, idola fori ; precisely illustrations of that vague biological use of 
the well-defined terms of exact science against which I have elsewhere strongly 
protested*. My own strong opinion is that biological conceptions can be accurately 
defined, and so defined measured with quantitative exactness. We are only at the 
beginning of this new scientific era at present and I may well fail with imperfect 
biological training to give proper definitions myself But I should be far readier 
to admit that there is nothing at all in the principle of homotyposis than to allow 
it to be placed in the same category as a " principle of symmetry " = a " principle 
of similar and simultaneous variation" = a principle which if it were not premature 
could be expressed in metaphors drawn from the " largely analogous phenomena of 
rhythmical vibration." This is the sort of language we know so well in mediaeval 
works on physics. As it was cast out from physics, so it must disappear from 
biology. 
* The Grammar of Science, 2nd Ed. p. 333. I can find no precise definition of these " principles " 
in Mr Bateson's Materials for the Study of Varia tion. 
