322 
GENETICS: S. WRIGHT 
Proc. N. a. S. 
and also some 4% more black within the colored spots. In the present 
paper only variations in the piebald pattern will be considered and the 
sexes will be dealt with separately. 
A record of the patterns of the guinea-pigs has been kept from the first 
by drawing the spots within a rubber-stamp outline. Only as much of 
the pattern as is visible from the back was recorded in this way before 
1915. Since that date, the patterns of both the back and belly have been 
recorded, but separately, making comparison with the earlier records 
possible. The amount of white in each case has been estimated by means of 
a piece of tracing cloth on which the area in the stamped outline is divided 
into ten equal dorsal parts and ten equal ventral parts, including the legs. 
Each guinea-pig is given a record such as B-R-W 2-5-3/X-5-5, meaning 
20% black, 50% red and 30% white on the back, a trace of black, 50% 
red and 50% white on the belly. In the present paper only the dorsal 
areas are considered. As the correlation between the amount of white 
on the back and belly is 0.86 and the back contains the most persistent 
center of color (the ear region) and almost the most persistent white (the 
nose) the grades, based on the dorsal part only, are believed to be prac- 
tically as satisfactory as grades based on the entire coat. 
Figure I shows the distribution of grades of white in three of the inbred 
families and in the control stock in 1916 to 1918. The representatives of 
60 
50 
40 
ZO 
20 
to 
_J 
\ 
F<3n 
Fan. 
\ 
Fc 
0 5 15 25 35 45 55 65 75 85 95/00 
FIG. 1 
Percentage distribution of grades of white in three inbred famiHes (39, 35, 13) and in 
the control stock (B) during 1916-1918. The percentages with less than 5 per cent 
white and with 95 to 100 per cent white are given double value, the class ranges being 
of half size. The few solid whites in Family 13 and B are arbitrarily given double 
value. 
