MENDELIAN EXPERIMENTS WITH FOWLS. 259 



But fcliere nvc also two, Nos. 2 and 5, in wliich the crest is very 

 slight, less than in the F,, No decided conclusions can be drawn 

 in this case. 



Comb. I have not yet observed any intermediates betweeii rose 

 comb and single. 



Silk)/ Plumage. I have not yet observed incomplete segregation 

 in this character. 



Many cases in which the results of crossing experiments are not 

 completely in accordance with the Mendelian theoi-y are mentioned 

 by Bateson in his ' Mendel's Principles of Heredity ' (1909), among 

 them being the double hallux, the leg-feathering, and the crest 

 of fowls. 



In the light of the fncts which I have recorded, the doctrine 

 known as Mendelisi.n cannot be said to be based on sufficient 

 evidence to justify the notorious dogmatism of its supportei's. 

 Mendelians assume that heredity is the transmission of unit 

 characters, which may sometimes combine to foi-m a new character 

 which is transmitted as a whole, ])\it that the units cannot be 

 subdivided. If subdivision occurs it is assumed to bd due to the 

 fact that a supposed unit was really compound ; if, however, the 

 process of segregation is at least in some cases not complete, but 

 each character after a cross is mingled with some fraction of the 

 opposite character, the assumption of units and all that is founded 

 upon it falls to the ground. It is possible that segregation is only 

 incomplete between characters which differ from one another in 

 degree and not in kind, for example between pigmentation and 

 absence of pigmentation in fowls. But if the doctrine now gene- 

 rally adopted by Mendelians of presence and absence is valid, it is 

 difficult to see how this difference could exist. Hitherto, Mende- 

 lian experiments liave been too exclusively carried oiit on the 

 assumption of indivisible characters, whether real or imaginary, 

 and the object kept in view has been to find, or invent, factors 

 wdiose complete segregation would agree wdth the observed results. 

 There is a promising field for research in the investigation of the 

 divisilulity of real characters. 



ncferences. 



Tegetmeier, W. B. — 1867. The Poultry Book. London : Rout- 

 ledge. 



Darwin, C. — -1876. Variation of Animals and Plants under 

 Domestication. 2nd Edition, Vols. I. & II. 



Bateson, W. — 1909. Mendel's Principles of Her-edity. Cam- 

 bridge University Press. 



Davenport, C B. — 1906. Inheritance in Poultry. Publications 

 of the Carnegie Institution of Washington, No. 52. Papers 

 of Station for Experimental Evolution, No. 7. 



Bateson, W., &l Punnett, R. C. — 1911. The Inheritance of the 

 peculiar Pigmentation of the Silky Fowl. ' Journal of 

 Genetics,' Vol. I. No. .3, p. 185. 



17* 



