SEX-LINKAGE IN FOWLS 505 
fowl. This seems to me to be one of the most difficult points 
in connection with the hypothesis here given to explain my results. 
It may be that there is some interaction between N and P, such 
that when both are present N cannot produce its effect. Then 
iNRPL would give red. This could be tested by raising large 
enoughnumbers from mating IV to find out the real F, proportions, 
or by testing a number of reds with Brown Leghorns and seeing 
if any of them gave brown duckwings in F, or F,. My principal 
evidence indicating that N is sex-linked was the fact that the 
females from mating II had red necks. But since they also had 
P, if the above hypothesis is correct, the only good reason for 
making N sex-linked is that it is probably identical with the 
factor described by Davenport (11) as being sex-linked. If 
it is not so linked, then some of the reds from mating III should 
also carry it, and that mating should, eventually, produce some 
brown duckwings.* 
Since I have no evidence that R or L is missing in any of my 
birds I shall simplify the following formulae by omitting them. 
In these formulae MM represents a male, Mm a female. 
I. Columbian Wyandotte  INPM INPM 
Brown Leghorn @ inpM inpm 
INE Nivnp ieee 
INPM inpm — gray 2 
II. Brown Leghorn inpM inpM 
Columbian Wyandotte 9 INPM inPm 
inpM INPM —gray & 
inpM inPm —red 9 
III. Brown Leghorn o& inpM inpM 
Red @ (gametes) inPM inpMinPm inpm 
inpM inPM —redo& 
inpM inpM —brown o (not seen) 
inpM inPm —red 9 
inpM inpm —brown Q (not seen) 
’The real solution of this difficulty may be that J and N are coupled. 
