118 Francs B. Sumner 
1 The tails of the warm room individuals are much longer than 
those of the cold room individuals. ‘This difference amounts to 
27.1 per cent for the males, 33.0 per cent for the females, and 29.7 
per cent for the sexes combined. Indeed, the two types are so 
distinct that, but for a single individual, there would be no over- 
lapping of the polygons; i. e. (barring this single exception), the 
longest tail in the cold room lot was shorter than the shortest in the 
warm room lot. ‘These differences were so patent to the eye that, 
had the two lots of mice been mixed together accidentally, I am 
(ee ae Gal ie TGisliC Sau) ell adel 
Fig.2 Series of 1907-1908: weight at six weeks of age (sexes combined). Abscissas denote weight in 
grams; ordinates denote number of individuals. Vertically shaded areas represent warm-room ani- 
mals; horizontally shaded. areas represent cold-room animals. i 
sure that I should have been able to separate them again with com- 
paratively few mistakes. Contrary to the condition in the first 
year’s series, a greater difference is here shown by the females. 
2 The warm room males were on the average I per cent lighter 
than the cold room males; the warm room females, on the contrary, 
were 7.7 per cent heavier. Quite similar relations in respect to 
weight will be found in the series of the following year. The 
frequency polygons for weight show that two groups of individuals, 
having two different ‘‘modes,”’ are comprised in the cold room 
lot—a lighter and a heavier group. An analysis of the individual 
