272 



BIOLOGICAL LECTURES. 



definition implies a quantitative difference in the power of 

 transmission. A great difference may indeed be detected and 

 expressed without resorting to measurements ; but it will often 

 happen that there is true prepotency even if slight, and such 

 prepotency must go unobserved without the use of the quanti- 

 tative method. Then there is the problem, so important for 

 the question of species, of the relative potency of sports and 

 the normal form when mated. Even a slight prepotency, too 

 small to be detected qualitatively, may suffice to prevent the 

 sport from being swamped by crossing with the normal form. 

 Again, there is the question of telegony. Whether the first 

 sire influences subsequent offspring can be affirmed or denied 

 only by comparing the correlation between offspring and pre- 

 viously cross-mated mother with the correlation between off- 

 spring and previously pure-mated mother. If there is less 

 correlation in the first case than in the second, telegony exists. 

 The facts of xenia are to be investigated in the same way. 

 Still further, the phenomena of blending of parental characters 

 in hybridization, or of their alternative heritage, or their patch- 

 work intermingling — all these phenomena demand careful 

 quantitative study. 



Finally, even the development of the specific form in the 

 individual demands quantitative investigation. Many investi- 

 gators have already studied embryonic variation, but few quan- 

 titatively. The precise comparison of variability in the embryo 

 and the adult will be of importance on account of its bearing 

 on theories of selection and self-adaptation. The most impor- 

 tant results in this field are, however, clearly gained by the 

 quantitative study of variation in embryos subjected to varying 

 ■environmental conditions. The exact comparison of change of 

 environment with change in form will lead to a still more pre- 

 cise knowledge of the effect of external agents. So likewise 

 the quantitative studies made on the result of experiments to 

 produce race change will be the most striking. In fact, in the 

 application of combined experimental and statistical methods 

 to genetic problems, zoology will reach its highest development. 



