On Mendel's Laws. 
237 
as causes affecting the values of the constants of heredity, until now 
any statement as to numerical fixity seems reduced to the truism 
that the constants will always he the same unless for some reason 
they are different. What is required from a physical theory 
of heredity is that it should assign a meaning to the variations 
in the constants that do occur, enabling one, given the law of 
ancestral heredity for an organ, to state the relative influences 
thereon of fehe different agencies concerned—selection, in all forms, 
circumstance, arid so forth. That an ideally complete theory cannot 
come yet, may be conceded at once; that it is impossible in the 
present state of biology to form a quantitative theory, founded on 
clear and definite physical conceptions, which will carry one some 
steps on the way, I do not believe. 
BIBLIOGRAPHY, 
In the preceding articles I have only given definite references 
to the two volumes mentioned in the first note: the following 
list includes all those that are necessary for the points referred 
to as regards the Law of Ancestral Heredity, etc. 
(0 
(*) 
( 3 ) 
(4) 
o 
( 6 ) 
(7) 
( 8 ) 
Francis Galton, F.R.S. “ Hereditary Genius.” 1st edn. 
Macmillan, 1869. 
Francis Galton, F.R.S. “ Natural Inheritance.” Macmillan, 
1889. 
Francis Galton, F.R.S. “The average contribution of each 
several ancestor to the total heritage of the 
offspring.” (includes the work on Basset-hounds). 
Proc. Roy. Soc., Vol. 61, 1897. 
Piofessor Karl Pearson, F.R.S. “Regression, heredity, and 
panmixia.” Phil. Trans. (A), Vol. 187, 1896. 
Professor Karl Pearson, F.R.S. “ On the law of ancestral 
heredity.” Proc. Roy. Soc., Vol. 62, 1898. 
Professor Karl Pearson. “Genetic Selection. Inheritance 
of fertility in man and of fecundity in thorough¬ 
bred racehorses.” Phil. Trans. (A). Vol. 192, 
1899. 
Professor Karl Pearson. “ The Grammar of Science.” 2nd 
edn., 1900. 
Professor Karl Pearson with L. Bramley-Moore. “ On the 
inheritance of coat-colour in horses. On the 
inheritance of eye-colour in man.” Phil. Trans. 
(A). Vol. 195, 1900. 
Professor Karl Pearson with Miss M. Beeton. “ On the 
inheritance of duration of life and the intensity 
of natural selection in man.” Biometrika, Vol. 1, 
October, 1901. 
