126 Francis B. Sumner 
figures will be later combined, however, with certain of those given 
for the next group. 
The unmated males, measured at the age of 24 months, consti- 
tute the most important groupin the second year’sseries. ‘Table 6 
(A, B, and C) presents the measurements for these 43 mice. These 
measurements were all made after killing. 
Comparison of these figures with those given for the males at 
42 days is of course only possible in respect to two characters— 
weight and tail length. In order to determine accurately what 
changes have occurred in these, however, we must first combine 
the figures for the present group with the preceding group of 
“mated males,” since the two together comprise the entire col- 
lection of males which had been measured earlier in life.** ‘Table 
7 accordingly represents the mean weight and tail length for all 
males at the age of 25 months. 
TABLE 7 
Series of 1907-1908: All males at 24 months of age 
WEIGHT TAIL LENGTH 
| i | 
| Warm (29) Cold (27) Warm (29) | Cold (27) 
| | 
Meany tseeeel 17.176 | 18.396 | 77-41 | 63.33 
| 0.331 | 0.396 | 0.44 | 0.56 
Standard deviation... .| 2.646 3.053 | 3-54 4.28 
+0.234 +0.281 +0.31 +0.39 
Comparing these figures with those of the males at six weeks 
of age, we note that whereas the tails of the cold room lot have 
increased 16.9 per cent in the interval between the measurements, 
those of the warm room lot have increased only 12.5 per cent. 
There is thus seen to be a tendency to “catch up” on the part of 
the less developed organs, which has already been pointed out for 
24 In combining these figures an allowance is first necessary. The tail length of the dead mice was, as 
stated above (p. 103), obtained by a different method from that practised upon the living ones. I 
have found that in living mice of this size the tail is stretched on the average about 1.5 mm. during 
the suspension. This amount has accordingly been added to the mean tail length of the unmated ~ 
males before combining with that of the mated males. The resulting figure represents approximately 
the tail length which would have been obtained had all been measured alive. 
