Page:Proceedings of the Royal Society of London Vol 69.djvu/208

194 generally. The conception of heredity is tlms greatly simplified, and that phenomenon is seen in its true relation to the other phenomena of life, becoming merely a special case of the phenomenon of Division and repetition of parts.

This idea came first to me as it has perhaps to others when I was studying the phenomena of Variation in Meristic Series, and in writing on that subject I introduced an outline of the conceptions involved.* On that occasion I ventured to carry this reasoning a step further, as it seemed, and to suggest that the resemblance which we call Heredity may be a special cute of fit? phenomenon of Symmetry. The thought then expressed has been a constant companion ever since, and I have become more and more convinced that it is fundamentally true.

I should welcome Professor Pearson's paper inasmuch as it is an attempt the only one, so far as I know to emphasise and develop this conception ; for, like him, I am sure that it may provide the key to the nature of heredity, perhaps also to problems beyond.

Variation in some of its essential features may thus perhaps be reduced to a geometrical problem. One of the many factors or con- ditions of fraternal resemblance may be Symmetry of division, quanti- tative and qualitative. The reference to the phenomenon of Sym- metry seemed to me to carry the principle a stage further, and to show Heredity as a special case of a phenomenon, the conditions of which we may reasonably hope, in a measure, to apprehend in at least its simpler phases. Professor Pearson, on the contrary, avoids mention of Symmetry. This arises, I presume, from a desire to use a more general expression, and from a reluctance to appear to exclude from his comparison the relation between members of Linear or Successive Series, whose mutual relationship is not one of Symmetry in the ordinary sense. He would probably prefer to regard Symmetrical division as a phase or perhaps as a consequence of the phenomenon of the production of " undifferentiated like parts " occurring under special conditions.

I still think something is gained by inverting the statement and speaking of the likeness between the parts as a phenomenon of Sym- metry. In some respects Professor Pearson's mode of expression is preferable as being more comprehensive, but mine has the advantage of keeping before the mind the fact that it is in the Symmetry of c.ell- tlivision that the resemblance between relatives is presented in its simplest form ; and also that the axes along which the " like parts " are produced are frequently definite.

Thus, fraternal correlation in its most striking manifestation is seen in the simultaneous variations of Homologous Twins. t

181)4, lutrod. Sect, VII; and also p. 21.
 * For a somewhat fuller treatment see ' Materials for the Study of Variation,'

f See ' Materials,' pp. 559 and 560. Following the work of Driesch and others