88 HENRY H. DONALDSON 
increase. Assuming then that the terminal values are correct, 
that the second entry is aberrant and that the intermediate values 
are approximately normal, Dr. Hatai determined the formula 
for the curve which fits the observations. This formula is as 
follows: 
y = 0.00105 x + 0.548 log x + 0.476.......... (1) 
where x equals the body weight and y the cranial capacity in cubic 
centimeters. 
Examination of chart 3 shows at once that the three series of 
the European records do not run exactly with the line representing 
the Philadelphia series. Inspection shows that the order of the 
TABLE 17 
Mus norvegicus. Showing the mean percentage deviation in cranial capacity for 
each of the three European Norway series from the Philadelphia series taken as a 
standard 
E | MEAN PERCENTAGE 
eS | DEVIATION 
| 
ATS er Mee oes co &, ont ah tlt tee orotate A ee ear eee —0.4 
| Bay avo (ort, Nig eee Ss eee OR Ne Men bi wie Peer atm —2.5 
NVATIEN A103 baie he aR ae PR a ed eR St ats fe EN a ap ate | —3.3 
P NS GY ERNE ss ARE Oa Cuetec Ms Coch, oy oe | —2.1 
mean values from highest to lowest is Philadelphia, Paris, London 
and Vienna. If then we compute the mean deviation from the 
Philadelphia records for each of the European series given on the 
chart, we obtain the values entered in table 17. 
As table 17 shows, the average of the mean deviations for the 
cranial capacity of the European Norway series combined is —2.1 
per cent. It thus appears that all the European series for the 
Norway rat exhibit a smaller cranial capacity than the Philadel- 
phia series and that the most marked deviation occurs in the case 
of the London and Vienna series where the deficiency is 2.5 and 
3.3 per cent respectively. , 
For the Albinos, the Philadelphia series are also taken as the 
standard. The curve is represented by the continuous line in 
