An Introduction to a Biology 



that character which, like the elements of the chemist, can- 

 not be split up into simpler characters. I do not pretend 

 that my formulae of heredity describe the numerical results 

 obtained by jumbling a lot of my elemental imits together, 

 any more than you pretend that the Law of Ancestral Heredity 

 describes the phenomena exhibited by my units when dealt 

 with separately." 



The point that I wish to bring home to the reader is that 

 the statement that Mendelism deals with units and biometry 

 mth masses is not merely a brief summarising statement 

 which pleases the mind, but that it has an actual meaning 

 in relation to the facts ; that is to say, that the limits of 

 these units are not set by the imagination, but are discovered 

 by experiment. 



(c) Examples of the Confusion between Physiological 



AND Statistical Laws 



Having spoken this much on the difference between 

 physiological and statistical Laws of heredity, I propose 

 to consider a few cases where failure to perceive this differ- 

 ence has led to confusion. As I have already referred to 

 Castle's case, I will finish with it before I proceed to others. 

 He says :^ " The foregoing results show very clearly that 

 albinism conforms in the mode of its inheritance to Mendel's 

 law of heredity. The fact, however, must not be overlooked 

 that a somewhat different explanatio7i of its inheritance (I) 

 has recently been given, based on Galton's " law of ancestral 

 heredity." I shall not at this time enter into a detailed 

 discussion of Galton's hypothesis, which was an entirely 

 rational one in thejoryn in which it was originally proposed (2); 

 and quite in harmony with the phenomena of gametoijenesis (3) 

 as then interpreted. I have shown elsewhere- by a specific 

 test in the case of mice, based on the observations of von 

 Guaita, that Galton's law fails to account for the observed 

 facts (4) concerning the inheritance of albinism, but that 



1 Castle, ;0o, p. IG. « ibid., :03, p. 231. 



187 



