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PROFESSOR K. PEARSON AND OTHERS ON 
i-eciirring ideas. I shall call niidifFereiitiated like organs homotypes, indicating that 
they are types produced by the same mould or individual. Thus two leaves of the 
same tree, or two Idood-corpiiscles from the same frog are hoinotypes ; their resem¬ 
blance will l)e homotypic, and the character by which their resemhlance is quantita¬ 
tively measured will be the homotypic character. I shall speak of homotypic 
correlation and distinguish it from organic correlation—although, of course, the 
foi'iner is in a certain sense organic. By organic correlation I refer to the correlation 
between two different characters in the same f)rgan ; by homotypic correlation to 
the correlation between the same or different characters in a jjair of homotypes. 
If the same character, then the correlation is direct homotypic correlation ; if different 
characters, then the correlation is cross homotypic correlation. Lastly, the principle 
that homotypes are correlated, i.e., that variation within the individual is less than 
that of the race, or that undifferentiated like organs have a certain degree of 
resemhlance, I shall speak of as homotyposis. Thus homotyposis denotes not only 
likeness of the homotypes, hut that this likeness has probably definite quantitative 
limits. If my view lie correct, heredity is only a special case of homotyposis, any 
multiplication of cells is homotypical, and denotes a given degree of variation and a 
given degree of likeness. This does not “ explain” heredity, hut shows it merely as 
a phase of a much wider natural process. 
IV. Actual Data. 
Section I.— Leaves of Trees. 
(G.) The leaves of trees provide material for fairly easy computation without 
measurement. Thus we may count the veins on the leaf or the leaflets on the com¬ 
pound leaf, and ascertain the degree of resemhlance between leaves of the same tree. 
The variation is, however, in some cases very consideral)le, and the labour of forming 
the tables involving thousands of entries very great. Still the leaf-series are some 
of my liest, and considered as a whole, perhaps the most satisfactory. 
(7.) A. Ash (Fraxlnus excelsior). Numher of Pinme on Ijeaf. —My first series (i.) 
consists of 2G leaves taken from each of 109 trees by Dr. Alice Lee or myself 
The trees were nearly all large old trees, growing on the commons of Great and 
Little Hampden, Buckinghamshire. The leaves were taken as ffir as possible from a 
variety of branches all round the tree, and from different points on these branches. 
The labour of tabling and deducing the constants is due to Dr. Lee. The number 
of })airs = 70,850. 
My second series (ii.) consist of 26 leaves taken from each of 120 trees by Miss 
D. Fawcett, B.Sc. These trees, many of which were young trees growing in 
the hedgerows, were taken in the neighhourhood of Lyme Begis in Dorsetshire. 
The same rules as to gatliering were observed. Dr. Lee again undertook the labour 
of tabling and the deduction of the constants. The number of pairs — 73,000. 
