136 ELIZABETH HOPKINS DUNN 
Table 2 introduces the averages for the groups of rats, first 
according to sex, and finally as a whole. It shows the average 
weight, the average number of medullated nerve fibers, the aver- 
age areas of the largest nerve fibers in square micra, the average 
areas of their axis cylinders, and the ratio of these averages. 
It may be of interest to show how the individual rats of the 
selected series differ from such averages as have been established 
already for the weight-age complex. In a joint paper by Donald- 
son, Watson, and Dunn (’06) certain averages and extremes of 
weight by age were published, upon which I have drawn for a 
series comparable with the present series. These data are pre- 
sented in table 3 and are followed in table 4 by a compilation of 
the ages and weights of the rats of the present study. 
TABLE 3 
MALES FEMALES 
DAYS SA Was a a r — a — a), Ao 
Lightest Heaviest Average Lightest Heaviest | Average 
| 
7 73 12.7 9.2 ee sls Dee a Sez 
149/74 490 17.6 15.2 13.5 18 a ereRG 
37 28.5 48.0 37.8 29.8 47.4 | 39.5 
76 89.8 157.5 121.3 89.6 131.6 | 2 104 
131 132.4 249.2 202.5 151.2 DAG 1°. | 7 eee 
178 167.9 291.2 239.4 153.0 915.0 “| “aol 
256 190.5 310.0 265.4 | 
TABLE 4 
MALES FEMALES 
DAYS ¢ r —s es 
Lightest Heaviest | Lightest Heaviest 
| 
=a = | = —— ——— 
7 8.90 9.75 8.25 8.93 
14 | 20.73 21.93 19.98 | 21.85 
36 31.20 52.65 39.17 45.30 
75 149.40 189.70 130.31 143.10 
132 | 260.00 274.00 161.00 167.51 
180 227 .60 302.00 200.00 225.00 
270 330.68 | 349. 41 165.85 187.96 
