680 HENRY H. DONALDSON 
From the foregoing we are justified in concluding that there is 
a seasonal change in the relative weight of the central nervous 
system of the leopard frog, R. pipiens, and that this occurs 
regularly each year and in frogs taken from widely separated 
localities. 
Moreover, if we know in any case the value of C for a colony 
of frogs at a given date, it is possible in accordance with these 
results to determine approximately what the value will be for 
other representatives of the same colony, at any other season of 
the year. 
Nevertheless in the first instance, the values of C for a given 
colony must always be determined by direct observation. We 
have seen that at similar dates the value of C for the Brandy- 
CHART 4 
16- PER CENT ° 
12+ CHANGES IN THE 
gL VALUE OF C. 
Ory x xo 
1 
_L 1 — et 1 =f ! {ee 
FEB. MAR. APR. MAY. JUNE. JULY. AUG. SEPT. OCT. NOV. DEC, JAN. 
Chart 4 Based on data in table 8. Also giving an ideal curve about which the 
several records are grouped. 
® Records from Chicago series. 
° Records from Minneapolis series. 
x Records from Brandywine series. 
wine frogs is 24.0, for the Chicago frogs 24.7 and for the Minne- 
sota frogs 28.1. The differences between these series I refer to 
the general effect of the external conditions (= food supply, 
abundance of water, etc.) but whatever the explanation is, such 
differences must always be anticipated. 
Further, the individual variation in this character is large 
so that all determinations should be based on data from groups, 
and not on single cases. 
On the other hand, although the frogs from a given locality 
or station may have the central nervous system developed in a 
proportion different from that found in frogs from another local- 
ity, yet frogs from the same locality tend to remain constant 
in this character. 
