ami other Conceptions of Bioloiji/. 19") 



It is true that the geometrical relations of members in Successive 

 Series are not included in the term Symmetry,* hut the distinction is 

 largely one of degree, and the transition from one to the other is of 

 frequent occurrence. Similar organs may l>e repeated in one species 

 in radial series, while in an allied species the same organs by 

 differentiation of an axis stand in succession to each other, as every 

 naturalist knows. 



Professor Pearson writes (p. 291) : " When we ascertain the sources 

 of variation in the individual, then we shall have light on the problem 

 of fraternal resemblance." May we not also say that when we ascer- 

 tain the conditions of asymmetrical division we shall have light on the 

 problem of fraternal variation ? 



I introduce this reference to my own method of expression partly to 

 show how far I am in agreement with Professor Pearson on a main point, 

 and partly to emphasise the significance which the analogy between 

 Repetition and reproduction gains by the reference to Symmetry. 



Theoretical considerations in mathematical form are put forward by 

 Professor Pearson as tending to the belief that the numerical value 

 for homotypic correlation will, on an average of cases, approximate 

 to the average value found for fraternal correlation. 



The reasoning is beyond me, but I gather that the argument, by the 

 introduction of appropriate assumptions, amounts to a proof that if the 

 characters of the offspring, as measured by their deviations, depend on 

 those of the germ-cells of the parents, then the characters of the 

 repeated parts (or undifferentiated like parts) formed by that offspring 

 will similarly depend on those of the germ-cells ; and it would then be 

 expected that the correlation between those repeated parts of the sscme 

 individual would be similar in intensity to that between the germ-cells 

 of its parents. Whether the assumptions are justifiable I am noB able 

 to judge, as I do not properly understand them. 



The resemblance or correlation between " undifferentiated like 

 parts " is, then, regarded as a phenomenon similar to the correlation 

 between brothers. The latter correlation has been investigated by 

 Professor Pearson in a number of heterogeneous cases, and has been 

 found to vary from '1973 to 'G934, where is zero and 1 denotes 

 complete correlation.! The mean value approaches '45. He pro- 



on the artificial production of Double Monsters, we must regard the relation 

 between Homologous Twins as of the same nature as that subsisting between the 

 right and left halves of a bilateral organism. 



* It would be easy to suggest terms better adapted to the expression of these 

 conceptions, but to do this at present is premature. When it becomes necessary 

 to do so I anticipate that the largely analogous phenomena of rhythmical vibra- 

 tion will provide ready metaphors from which to construct a terminology well 

 adapted to denote the various phenomena of Merism. 



t Both here and in the coefficients of " homotyposis" reasons are given for sup- 

 posing that some of the greater departures from the mean may be explained away. 



