An Introduction to a Biology 



among the leaves or are digging among the roots. It may 

 or may not be that what we learn by the former method is 

 all that we shall ever know, and that we shall find nothing 

 by our digging ; but be this as it may, I hold that it is essen- 

 tial to progress in discovery, no less than to clearness of 

 thought, that we should know which of the two we are 

 doing. 



(d) DESCRIPTION OF A METHOD OF DEALING WITH THE 

 MATERIAL OF A BREEDING EXPERIMENT IN SUCH A WAY 

 THAT THE DATA OBTAINED MAY BE USED TO TEST THE 

 VALIDITY BOTH OF MENDEL'S AND PEARSON'S LAW 



When I had finished my last paper on my hybridisation 

 experiment with mice 3 I was still of the opinion that Men- 

 delian and biometric Laws of heredity were mutually ex 

 elusive, and that if I could discover which of the two was 

 true, I should be making a forward step in our knowledge 

 of heredity. I therefore devised an experiment which was 

 destined to settle this question ; and wasted a year in carry- 

 ing it out. As soon as I discovered the true relation of 

 the two Laws I devised a method of dealing with my ex- 

 periment, of such a kind that the results could be utilised 

 by the Mendelian or the biometrician to test his own par- 

 ticular Law ; for the stringency with which the mice were 

 selected in the previous part of the experiment rendered 

 the results useless for anyone who wished to test the Law 

 of Ancestral Inheritance by them. 



What was wanted was some device to ensure the random 

 mating of the mice, and at the same time to ensure the possi- 

 bility of tracing all the ancestors and all the offspring ; in 

 fact, all the relations of every degree of every individual 

 mouse ; the second condition had been fulfilled in the pre- 

 vious part of my experiment, but the first had not, because 

 the different kinds of mice had been rigidly selected. 



The method by which I mated the mice at random was 



3 Darbishire, :04a. 

 192 



