CHANGES IN WEIGHT OF CENTRAL NERVOUS SYSTEM 693 
bear on the phenomena of growth as shown by vertebrates in 
general. The curve for the growth of the central nervous system 
of the frog as given in chart 5 has the general character of the cor- 
responding curve for a mammal; but as is evident, this curve in 
the case of the frog must repeat itself from year to year, so that 
if we should plot the entire curve for the span of life, rather than 
for a single season, it would be represented by a sinuous ascend- 
ing line in which the sinuosities would probably diminish towards 
the upper end. 
If we turn now to general body growth, which is closely corre- 
lated with that of the central nervous system, it appears that the 
poikilothermous vertebrates as a group must show a seasonal 
variation in growth in all latitudes where there is any marked 
seasonal change, and that the phenomena of hibernation, with the 
concomitant effects with which we have to deal, represent merely 
a special case of this seasonal variation. 
If now we pass up the vertebrate scale we find in the temper- 
ate zones both hibernating mammals, as well as those in which the 
seasons seems to produce marked nutritional modifications, and 
finally we have Malling-Hansen’s observations (’86) on Danish 
children from 9 to 15 years of age which show that the growth in 
stature is mainly inthe third of the year between the middle of 
April and the middle of August, while the third comprised be- 
tween the middle of August and the middle of December is the 
one in which they gain nine-elevenths of their annual increase in 
body weight. This leaves the remaining third from mid-De- 
cember to mid-April, z.e., late winter and early spring, as the one 
in which very little growth of any sort occurs. This seems to 
link the rhythmic growth in the frog with that in man. To be 
sure there are at present but very few data available, but such as 
we have suggest that within the annual cycle we should expect 
even in the higher vertebrates a distinct rhythm corresponding 
to the responses of the poikilothermous vertebrates, and still exhib- 
ited even by the group in which the regulation of temperature 
has been more or less completely attained. 
Just one point more. The rate of growth in the frog, more 
than doubling its body weight for three successive years (as far 
as we have observations) shows that the rate in the frog does not 
