CHANGES IN WEIGHT OF CENTRAL NERVOUS SYSTEM 681 
This last statement is supported by my observations on the 
two European species, R. esculenta and R. temporaria, as given 
in table 9. 
As is seen, the value of C in both the European forms is less 
than in the American R. pipiens (Donaldson, ’08 and ’10). 
The point to be specially illustrated in table 9 is, however, that 
frogs from the same locality maintain the same values of C. Thus 
both series of R. esculenta, taken from the same station at Zurich 
and examined in July, but with an interval of five years, show 
values of C nearly alike. 
TABLE 9 
| VALUE OF C 
| NUMBER OF : 4 Fie Sh ews 
POR | SPECIMENS BEAMINED. Probable 
Mean error of the 
mean 
Rresculentascceer sae eee | 11 July 20, ’04 23.8 | +(). 46 
Rescuilemitan $3. yas. 11 | aluly 6, 709 23at +(0.36 
Its LEMMON oo ooeocue see 12 July 1, ’04 22.8 | +£0.47 
I, WEMO NOMEN oe gee ge eno c|| 16 August 20,709 21.8 | =+0.26 
On the other hand, the two series of R. temporaria from the 
same station at Liverpool, give on July 1, 1904, 22.8 and on August 
20, 1909, 21.9, a fall of about 4 per cent in the value of C, which, 
as explained above, is the sort of change to be expected, although 
the amount of it is larger than we should have predicted. 
Il. THE BIOLOGICAL INTERPRETATION OF THE SEASONAL 
CHANGE IN THE RELATIVE WEIGHT OF THE 
CENTRAL NERVOUS SYSTEM 
In order to form a proper picture of the manner in which this 
change in the relative weight of the central nervous system as 
just described is brought about, it will be necessary to obtain a 
notion of the growth changes in the entire frog during the active 
period of each year. At present only two sets of observed facts 
are available: (1) The change in the percentage of water. (2) 
Changes in length :—but from these latter, changes in body weight 
can be fairly inferred. 
