Heredity, Differentiation, awl otlicr Conceptions of Biology. ]().'* 



(d.) Elongation accompanying rises of internal pressure. 

 (e.) Pulsatile increase of volume during sudden brief elevations of 

 internal pressure. 



The discordant results obtained by various observers (Marey, Roy, 

 and others) as regards the distensibility of arteries, are in large measure 

 explicable by the absence or presence (in varying degree) of post- 

 mortem contraction in the arteries they used in their experiments. 



" Heredity, Differentiation, and other Conceptions of Biology : a 

 Consideration of Professor Karl Pearson's paper ' On the 

 Principle of Honiotyposis.' ' By W. BATKSON, M.A., F.R.S. 

 Received January 25, Read February 14, 1901. 



In his paper on " Honiotyposis,"* of which an abstract appeared in the 

 ' Roy. Soc. Proc.,' vol. 68, p. 1, Professor Pearson raises an issue of extra- 

 ordinary importance. In any attempt to perceive the true relation of 

 variation to differentiation, and to analyse the essential similitude 

 existing between Heredity and Repetition of Parts, we reach a funda- 

 mental problem of biology. Little has thus far been done towards eluci- 

 dating this problem or even towards formulating it. The appearance 

 of Professor Pearson's remarkable memoir may perhaps therefore with 

 profit be taken as an occasion for considering critically some aspects of 

 these questions. 



It is impossible to write of Professor Pearson's paper without 

 expressing a sense of the extraordinary effort which has gone to its 

 production and of the ingenuity it displays. But on careful examina- 

 tion it will, I think, be seen that in the light of known facts there is. 

 serious doubt whether the determination of what Professor Pearson 

 calls the average homotyposis of " undifferentiated like parts " can be 

 attained by his observations, and that there is even graver doubt 

 whether, if it was attainable, such a value would have any natural 

 significance. In the course of this consideration it must, I think, also 

 appear that the comparison he attempts between the average homo- 

 typosis of " undifferentiated like parts " and average fraternal corre- 

 lation in families is incorrectly instituted. 



At the outset I wish to express the conviction that the leading idea 

 which inspired and runs through the work is a true one. Professor 

 Pearson suggests that the relationship and likeness between two 

 brothers is an expression of the same phenomenon as the relationship 

 and likeness between two leaves on the same tree, between the scales 

 on a moth's wing, the petals of a flower, and between repeated parts 

 * ' Phil. Trans.,' A, 1901, vol. 197, p. 285. 



