22 SIZE INHERITANCE IN RABBITS. 



cies, and frequencies of characters, but it has not contributed to the 

 biological understanding of these facts. Its laws are applicable to 

 great masses of individuals from mixed matings, but they do not apply 

 to individual pedigrees. They describe facts of inheritance mathe- 

 matically instead of analyzing them biologically. And it is only by 

 this latter method that the real mechanism of inheritance and of species 

 formation can be finally revealed. 



From a mathematical standpoint Brownlee (1911) has shown that 

 the coefficients obtained by the statisticians would be expected in 

 populations if stature, for instance, depends upon several independent 

 Mendelizing factors. His conclusions are as follows : 



" (1) If the inheritance of stature depends upon a Mendelian mechanism, 

 then the distribution of the population as regards height will be that which is 

 actually found, namely, a distribution closely represented by the normal curve. 



" (2) There is nothing in the values of the coefficients of inheritance found 

 by Sir Francis Galton and Professor Pearson which can not be explained on 

 the basis of Mendelian inheritance." (Page 255.) 



Lock (1906) states in general terms that crosses between corn strains 

 of different heights gave an obviously intermediate first generation; 

 that a number of these crossed back to the smaller parent gave a 

 remarkably uniform generation, in which were found no signs of segre- 

 gation into two groups, as should be expected if Mendel's law were to 

 be applicable. He regards this condition as possibly due to a homogen- 

 ous development of the germ cell. As no measurements were taken 

 and as the number of individuals observed is not given, one may very 

 well question the uniformity of this back cross. The work of Emerson 

 stands in direct opposition to these results. 



It is interesting to note that immediately preceding the discussion 

 of height crosses, Lock describes the case of crossing dent and flint 

 varieties of maize, which on similar evidence has been interpreted by 

 East and Hayes (1911) as due to the action of two or more similar 

 independent factors. This work was done by Lock before Nilsson- 

 Ehle's discovery, so it was not even suspected that the great variability 

 in the second generation might actually be due to segregation; instead, 

 it was supposed that the occurrence of segregation could not be proved, 

 as the variability masked its possible presence. 



A far more exact and important investigation on a size character 

 that was believed to "blend" in inheritance, is that of Castle and 

 Walter (1909) on the length of rabbits' ears. Crosses between rabbits 

 with long lop ears and with short erect ears gave offspring with inter- 

 mediate ear lengths. These crossed with the long-eared parents pro- 

 duced a second generation with ear lengths intermediate between the 

 Fi and the long-eared parent ; Fi animals crossed with the short-eared 

 parent gave a second generation with ears half way between these 

 parents. Other crosses between crossed animals consistently gave 



