METABOLIC ACTIVITY OF NERVOUS SYSTEM 49 
values are arranged according to the body length of the snapper 
(table 1) and there is no noticeable tendency for the lower values 
of the percentage of water to occur more frequently among larger 
fish, or vice versA. From this we infer that so far as the present 
data are concerned, the percentage of water in the small and 
large fish is nearly identical within a wide range of body length, 
and therefore the percentage of water does not vary regularly 
with the length or size of the fish. The average of 64 deter- 
minations gives the percentage of water as 78.61 per cent. 
This wide variation in the percentage of water I am unable 
to explain at the present moment. It was thought at first that 
the method of capture, particularly the use of dynamite, might 
be responsible for it. Careful examination however (see re- 
marks in table 1) of the table shows at once that such is not 
the case, and these wide variations are not correlated with the 
method of capture. It is true that the cranial cavity of the fish 
contains liquid as well as a jellylike substance, and the adhesion 
of particles of this substance may alter to some extent the per- 
centage of water, but this factor is too insignificant to cause the 
wide variations shown in the table. 
One other factor, though it appears to be important, cannot 
be readily tested, namely, masked age; that is a failure of the 
size and weight of the fish to indicate the age. We have no way 
to determine the age of the gray snapper. It may be that the 
size of the fish shows a wide range of variation for any given age. 
If size was positively correlated with age, then the low percentage 
of water would be given by the older fish, and vice versa. There- 
fore should we be able to arrange the data according to the ages 
of the fish, not the size of the fish as has been done, the values 
for the water should arrange themselves in a regular descending 
order with increasing age. ‘This is, however, a mere speculation 
and must wait the test of future investigation. 
Still another possible factor is the low grade of organization 
of the fish brain compared with that of the higher vertebrates. 
It is conceivable that owing to this low grade of organization, 
the structural maturity, or especially the processof myelination, 
may not progress regularly, and that within the same size or at 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, No. 1 
