BRAIN WEIGHTS OF RATS 561 
TABLE 3 
Fy GENERATION BRAIN WEIGHT GMS. 3 
~o & 
= a 
ae aril ead Sea sce) Se a : : 3 
Body length Tike eae vr lear emo SSS, ST Sea eee 
aa) wD oo) i [oe] ° So i) n oo a a i 
or — — — — rol an aN nN ins | & Ss 
mm. 
130-140 1 1 illest) 
140-150 6 1 TNs Ae TAG 
150-160 2 1 3 2 il 1 10 | 1.67 
160-170 2 1 5 3 Hal |) al 7} 
170-180 it 4 9 1 Se eee 
180-190 2 2 8 8 ih 1 28), UES2 
190-200 2; Pah Aut 8 D 1 26 | 1.89 
200-210 8 a 3 2 20 |} 1.95 
210-220 1 1 i 5 2, 5 1 16 | 2.06 
220-230 1 1 6 il 1 aera OS 
230-240 it Dy 3 | 2.08 
Frequency 
brain weight........ 3 C14 | 88 lP35m | eon elu 2 TARR crete 
hybrid generation and thus the brain weights occupy an inter- 
mediate position between the values given by the norway and 
albino rats and are like those of their immediate ancestors. 
The distribution of the individual brain weights in F; rats is 
similar to that of the F; rats and the concentration is greatest 
round the mean value. The frequency’ distribution of the 
brain weights in F, rats is best shown in chart 2 where observed 
frequencies are compared with those computed by the fol- 
lowing formula for the normal probability 
= Ot Ale em 
FREQUENCY CURVES 
Particular interest attaches to the frequency curves (chart 2) 
given by the brain weights in both the F, and F, series. The 
observed frequency distribution is closely represented by the 
normal probability curve; that is the distribution is symmetrical 
around the mean brain weight. I have shown in a previous 
paper (Hatai, 11) that the symmetrical distribution of the 
