INHERITANCE OF COAT-COLOR IN CATS 545 
occurrence of the rare tortoiseshell male. In 1913 he gave a 
further discussion of the subject and an excellent summary of 
data collected from fancy breeders. In 1914 he suggested non- 
disjunction of the sex-chromosomes in oégenesis to explain the 
matroclinous black females. These explanations are all more or 
less unsatisfactory for one reason or another, as admitted by 
Doncaster and by Little. 
I have pointed out (1915) that the hypothesis of simple sex- 
linkage first suggested by Little may be sufficient to account for 
the conditions if it be considered that the heterozygotes, which 
must be females, vary from black through various degrees of 
yellow-spotting to solid yellow. In the male, presumably, con- 
ditions are much more stable, as it is impossible to have a het- 
erozygote. Thus I have suggested that a gametically yellow 
male (YX —) may become tortoiseshell by extreme selection of 
black extension factors, while a gametically black male (yX —) 
may become tortoiseshell by an extreme selection of yellow ex- 
tension factors. The possibility is of course not excluded that 
there may be a single factor or particular combination of factors 
that produces yellow-spotting in the male. 
Ibsen (16) has suggested close coupling of two pairs of sex- 
linked allelomorphs, and attempts to explain anomalies by cross- 
ing-over. This does not account for all the results, however, as 
he himself points out. 
The data concerning the tortoiseshell problem which I have 
gained from my experiments are as follows: 
A long-haired cream male (8) (a.b.m.Y)? was crossed (12) 
with an intense strippd tabby (25) (A’.B.M.y). There resulted 
one maltese (a.B.m.y) and two intense striped tabby (A’.B.M.y) 
males and one blue and cream (a.B.m.Yy) female. 
The same male was crossed twice (9 and 30) to a black (20) 
(a.B.M.y). There resulted three black (a.B.M.y) and two mal- 
tese (a.B.m.y) males and two orange and black (a.B.M.Yy) and 
three blue and cream (a.B.m.Yy) females. 
2 The genetic formula includes only factors known to be present. The duplex 
condition is not expressed except in the case of the sex-linked pair Y—y in which 
dominance is variable. 
