AN ANALYSIS OF THE EFFECT OF SELECTION. 43 
5. PLuMace AND Tor CHARACTERS IN POULTRY. 
We are referred to the observations of Bateson and Davenport 
for these cases. In one instance it is stated that Davenport has shown 
that ‘imperfection of dominance” and of segregation are the rule in 
poultry. The question of imperfection of dominance is not apropos 
in this connection. As Castle has said, regarding another case: 
WS 5 . if black is crossed with brown, the crossbreds are apt to develop 
in their coats more brown pigment granules than do homozygous or pure 
blacks. Nevertheless, we have no reason to question the entire purity of 
the gametes, both dominant and recessive, formed by such cross-bred black 
animals. It is the dominance, not the segregation, which is imperfect.”’ 
(Castle, 1911, p. 91.) 
That F, results do not bear on the question has been shown by 
Bateson (1909), who says with regard to polydactylous fowls: 
“Tt might be pointed out that when, as in these examples, the abnormal 
result is clearly perceptible in F,, no question arises as to the occurrence of 
an imperfect segregation. The peculiarity is evidently zygotic, and is caused 
either by some feature of zygotic organization, or by the influence of external 
circumstances.” (Bateson, 1909, p. 251.) 
Moreover, in any case involving irregularities in dominance, im- 
perfect segregation in crosses between different breeds would be very 
difficult to demonstrate. 
6. MERINO SHEEP. 
No reference to the data in this case are given. I have been unable 
to discover anything more definite than a few general statements by 
practical breeders regarding the effects of crossing Merinos. 
Bateson admits, in the passage quoted above, that this and the 
next case ‘‘may be ascribed to the interference of a multitude of 
factors.” 
7. FANTAIL PIGEONS. 
This case has been studied by Morgan (Morgan, Sturtevant, Muller, 
and Bridges, 1915, p. 186). The fantail type did not reappear in the 
comparatively small F, generation, but individuals not far from the 
fantail were obtained; and when the F,; hybrids were mated to fan- 
tails, several of the offspring fell within the range of the fantail race. 
Bateson’s “‘failure of a parental type to reappear in its completeness 
after a cross” is, then, scarcely applicable to this case. 
8 anp 9. DutcH Rassits AND Cases IN SWEET Peas. FRACTIONATION. 
These are the specific cases cited as illustrations of Bateson’s theory 
of “fractionation” or ‘subtraction stages,” of which he states that 
‘it is to be inferred that these fractional degradations are the con- 
sequences of irregularities in segregation.” In the case of the sweet 
pea, Bateson has pointed out that white flowers and the extreme dark 
