256 ANIMAL MORPHOLOGY 



index of correlation measures the degree of morphological kinship or 

 of physiological interdependence. Symmetry gains a quantitative 

 expression, and it is interesting to find that originally non-symmetrical 

 organs which have secondarily gained antimeric relations as in 

 animals that habitually lie on one side gain a very high index of 

 correlation. Thus 1 find in the scallops (Pect en) , which are lamelli- 

 branchs that have come to lie on the right side, the index of correla- 

 tion between the dorso-ventral and antero-posterior diameters is 

 97 per cent, whereas the correlation between the breadths of the 

 right and left valves is only 86 per cent. As heredity is only one 

 phase of correlation, the inheritance of characteristics can, by the 

 new methods, be exactly measured. It is demonstrated that there is 

 such a thing as prepotency of one parent, and that heredity is weak- 

 ened by change of sex. It is shown that mental and physiological 

 characteristics are inherited exactly like morphological characteristics : 

 and that the relationship between the leaves of a branch or the zooids 

 of a colony is like that between brothers of a family. We learn that 

 all inheritance is not all of one kind; that certain characteristics, 

 like stature and skin color, blend in the offspring; while others, like 

 the coat color in mice, refuse to blend, and may be inherited according 

 to Mendel's law. 



By mathematical analysis the selection of particular characteristics, 

 or those of a particular degree of development, has been demonstrated, 

 and the exact effect of the selection process upon the frequency poly- 

 gon has been made clear. Extreme variants are often annihilated, 

 although in other cases the position of the mode is shifted. Finally, 

 through quantitative studies the existence of local races has been 

 clearly proved the degree of their differentiation and its depend- 

 ence on environmental conditions has been measured. It has been 

 shown that a characteristic does not remain the same in all localities 

 and under all conditions, but may become slightly altered. This fact 

 speaks strongly for the contention that new species may in some 

 cases have arisen by the summation of infinitesimal differences 

 that not all evolution is by mutation. 



In concluding this address I am impressed by the fact that to-day 

 any science ramifies in all directions toward every other. There can 

 be no doubt that the most fruitful work in any science is to be done 

 in the border-line between it and some other science. There is another 

 corollary to this close interweaving of the sciences, and that is that 

 the existing classifications have become antiquated. Our university 

 departments, our societies, and our journals still, for the most part, 

 draw the old lines. Yet the true work of science has, I apprehend, 

 overleaped the barriers of these classifications, and the best workers 

 will in the immediate future be no longer botanists, or zoologists, or 

 chemists, or mathematicians, but will be interested in particular sub- 



