198 Mr. W. Bateson. Heredity, 'Differentiation, 



ter of a hundred corpuscles in each of many Frogs. Find the correla- 

 tion due to the individuality of the Frog. How can we determine 

 whether in some of the individuals we have used there may not be 

 differentiation such as was found in Nigella, so that the parts are not 

 really " undifferentiated like parts " ? Would not such irregular 

 differentiation change the mean correlation between the corpuscles 1 



Would not the fear of such an error practically lead to the exclusion 

 of cases of suspected differentiation ivhir.h ought to be included in calcu- 

 lating the average 1 Is it not certain that differentiation in important 

 characters may take place in exactly the masked way I have referred 

 to 1 If, for instance, we could count granules in the corpuscles and work 

 out their homotypic correlation for these numbers, might not we have 

 among our individuals some which had specialised corpuscles absent 

 in others ? 



Again, does not individuality show itself by change in the degree of 

 differentiation among homotypes 1 ? Can we frame a definition of 

 variation which will exclude such changes 1 



A represents a radially symmetrical organism in which we may 

 study the correlation in lengths of the radial septa and determine how 

 much is individual or homotypic, and how much racial. If the radial 

 symmetry were always perfect and the specimens merely of different 

 sizes, the racial and homotypic 'correlations would be alike, unity. But 

 suppose the population consists partly of (i) approximately radially 

 symmetrical specimens ; (ii) quite irregular specimens like B ; (iii) of 

 specimens whose forms are controlled by an incipient differentiation of 

 any axis tending towards such a form as C.* How would Professor 

 Pearson's methods determine the true homotypic correlation in this 

 population 1 



Suppose that in a polychaet, say a Syllid, there is marked differentia- 

 tion between segments at the anterior and posterior ends separated by 

 hundreds of segments apparently undifferentiated, bearing append- 

 ages similarly undifferentiated. We may determine the homotypic 



* I have no doubt that a study of the CoraJs, say, would provide actual examples 

 of such a population. May not some Mushrooms be in just this state ? 



