118 
shows but 3.04 volumes. In the case of No. 1, taken at 
10:35 o’clock in the morning, with the sky covered with 
fleecy clouds, the amount of light was probably at least as 
great as in the case of No. 10, taken under a clear sky at 
sunset. 
While such evidence cannot be regarded as conclusive, 
it is, nevertheless, the only evidence now obtainable, and 
seems to indicate that at Frankfort and the Manitous the 
plankton is at this time of year about two and one-half 
times as abundant as at Ludington. 
Turning to the Detroit River, we find at a depth of ten 
feet a volume of only 1.2 ¢.c. per 600 cubic feet of water, 
an amount only one-third to one-half as great as at Lud- 
ington, and one-fifth or one-sixth as great as at Frankfort 
and the Manitous. 
While more accurate and extended observations might 
modify the results for Frankfort and Ludington, this is in 
no way probable in the case of Detroit. 
The results mean that white-fish fry would find food only 
from one-half to one-sixth as abundant at Detroit as at 
Frankfort, the Manitous or Ludington. 
This is only a very imperfect sample of the work that 
needs to be done. The enormous interest involved in the 
fisheries of the great lakes and the heavy expenditures 
incurred in stocking the waters with white-fish and other 
fry, warrant a most careful and exhaustive examination of 
. the biology of these waters. The problem should be at- 
tacked from every side and in the broadest scientific spirit. 
It is necessary to know accurately the kind of animals and 
plants inhabiting these waters, the numbers of each kind 
in a given volume of water, the variations in these numbers 
due to season, locality and other conditions. It is neces- 
sary to know the food of each kind of animal, its enemies 
and life history. The chemical composition of the water, 
the changes of temperature, at various seasons and at all 
depths, should be investigated, In short, every kind of 
