320 GENETICS: S. WRIGHT Proc. N. A. S. 
P = poYo/sm tan = l/(ctn ka - tan kl), tan ka = kro 
I enclose the following errata in my article on norns cited above: 
PAGE EQUATION FOR READ 
k . k 
276 4 —t —i 
2V 27r 
277 13 UV UV 
278 17 UV, au UV, olv 
278 19-20 d d 
281 above 36 Zi ^ ck''\ Zi = eib^j 
281 after 37 U.K. H.F. 
d^p dp d^p dp 
282 — + m — + p = 0, — — m — + k% = 0 
vn^ vn dx^ bx 
mx 
p = e~V4— ^==^1^ cos kx + B smkx\ p = e ^ {A cos k^l I '-{m/2kY.x 
+ 5 sin V 1 - {m/2k)\x\ 
mx 
+ r> sin i^Vl — (w/2;fe)2.:c) 
ra£ RELATIVE IMPORTANCE OF HEREDITY AND ENVIRON- 
MENT IN DETERMINING THE PIEBALD 
PATTERN OF GUINEA-PIGS 
By Wright 
Bureau of Animal Industry, United States Department of Agriculture 
Communicated by R. Pearl, March 17, 1920 
The Bureau of Animal Industry has been carrying on an experiment 
on the effects of inbreeding on guinea-pigs since 1906. Twenty- three 
families were started successfully from as many pairs and were main- 
tained wholly by matings of brother with sister. Another stock from 
the same source has been maintained as a control, without mating even 
second cousins. 
A number of color variations were present in the original stock and 
most of them kept appearing during the early history of each family 
as the result of Mendelian segregation. After a number of generations, 
however, a certain color became fixed automatically within each inbred 
line. In some cases an entire family came to produce only one color. 
In most cases, the families became broken into a number of sub-families, 
each characterized by a particular color. 
The original stock consisted largely of tricolors. Conspicuous differ- 
ences in the average amounts of white and yellow appeared among the 
inbred families from the first, proving the existence of hereditary differ- 
ences in pattern. Contrary, however, to the case of the qualitative differ- 
ences in color, no types of pattern ever became at all well fixed. Varia- 
