Vererbung, Variatiob, Mutation. 91 



Rocks whicli has been used in all the work in breeding for egg production has 

 become in any way deteriorated through the action of environmental or otlier 

 factors. It is furtlier specifically shown, by an experiment in out-crossing invol- 

 ving a large number of individuals, that the infusion of "new blood" into this 

 stock failed to produce any cliange in the egg production of the progeny. Such 

 a result makes it impossible to suppose that the degree of Inbreeding practiced 

 during the mass selection experiment can have had anything whatever to do mth 

 the results of that experiment. 



In the laying year 1907 — 08 a new plan of breeding was adopted as a 

 working hypothesis to be tested by experiment. This plan is based on the em- 

 ployment of individual pedigree records and has its theoretical foundation in the 

 genotype concept ofJohannsen. Ib involves the following factors: (a) That the 

 egg record of an individual hen gives no definite indication whatever as to what 

 the probable laying of her daughter will be. (b) A flock of hens, no matter 

 how "pure bred" it may be, is really not a homogenous, unitary aggregation, 

 but instead it is made up of a varying number of lines or strains, each of which 

 tends to breed true to a certain or definite degree of egg productiveness or fe- 

 cundity. (c) When mass selection alters the population type it does so by a 

 process of isolating from the mixture certain strains wliose own types are dif- 

 ferent from the original general population type and which differ in the direction 

 toward which selection is made. 



It is shown that by the application of this plan of breeding it has been 

 possible to isolate from the same stock of birds, which was used in the mass se- 

 lection experiment, pedigree lines or strains which for five generations (the time 

 covered by the experiment to date) have bred uniformily true to definite degrees 

 of egg production. From the evidence in hand it appears to be the case that 

 fecundity is inherited fundamentally according to Mendelian principles. There 

 is clear evidence that high fecundity and low fecundity segregate definitely fol- 

 lowing crosses between breeds of poultry bearing these characters as definite 

 breed characters. Further studies on this phase of the problem are now in pro- 

 gress. Pearl (Orono). 



223) Pearl, R., A note regarding Variation in the single combs of fowl. In: 

 Mendel Journal, 1, S. 189—195, 1911. 



Reply to criticism of a previous paper on the above subject. Gates (London). 



^24) Pearl, R., Inheritance in "blood lines" in breeding animals for 

 Performance, witli special reference to the "200 egg hen". In: Rept. 

 Amer. Breeders Assoc. 6, 317—326, 1911. 



It is pointed out that in such characters as speed in trotting horses, milk 

 production in cattle, and egg production in hens, the Performance record of the 

 individual is not a good criterion of the probable Performance of its offspring. 

 In other words, some individuales are prepotent in transmitting their peculia- 

 rities, while others are not. Thus the writer believes that high egg production 

 in hens is transmitted in particular "blood lines" or strains, in accordance with 

 the ideas of Johann sen. It is suggested that the explanation of prepotency may 

 lie in this fact together with a dominance of high genotypic performing ability 

 over a low degree of genotypic performing ability. Gates (London). 



225) Snow, E. C, The application of the Correlation Coefficient to Men- 

 delian distribution. In: Biometrika, Vol. VIII, No. 3—4, S. 420—424, 1912. 

 Criticism of Brownlee's paper in Proc. Roy. Soc. Edinb. 30. 6. 1911. 



Doncaster (Cambridge). 



