Page:Proceedings of the Royal Society of London Vol 69.djvu/212

198 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

of such a population. May not some Mushrooms be in just this state ?
 * I have no doubt that a study of the CoraJs, say, would provide actual examples