324 
Francis B. Sumner 
Unfortunately, only the weight and tail length of these mice were 
determined at the age of 6 weeks. At this time I did not realize that 
the foot and ear of a living mouse might readily be measured if the 
latter were etherized. The modification of foot-length and (with less 
certainty) of ear-length has already been demonstrated, however, for 
other lots of mice. Moreover, in the case of one set, comprizing over 
two hundred individuals, foot and ear measurements were made at 
the age of six weeks. The results of these latter measurements have 
Fig. 2. 
Curves showing tail length of parent mice at the age of 42 days. The upper line ( IV) represents the 
condition in the warm-room animals; the lower line (C) representing the condition in the cold-room 
animals. Ahscissas denote weight in grams; ordinates denote tail length in millimeters. The figures 
along the curves represent the numter of individuals in each size-group. 
been plotted in graphic form (Figs. 3 and 4) i) and will be of interest 
by way of comparison with the curves (Figs. 6 and 7) which have 
each brood which in weight approached most nearly the mean of the entire 
lot (»warm« or >cold<]. Each male used for breeding was derived from a 
different brood. 
1) This lot of mice comprized 80 cold-room and 129 warm-room individuals. 
They were the first offspring of the same parent brood as that just referred to, 
i. e. the parents of the generation to be discussed below. Since they were 
likewise subjected to considerable temperature differences, a possible cumula- 
