588 
BULLETIN OE THE BUREAU OF FISHERIES. 
only a small number of the larger crustacea were present, the total number in the catch 
was determined by direct count. One cubic centimeter of the diluted material was 
then placed in a Sedgwick-Rafter counting cell, and the protozoa and algae were enumer- 
ated in the usual manner. The results were reduced to the number of individuals per 
liter of water, and the diagrams were platted on this basis. For table xix the number 
of planktonts per liter was multiplied by a thousand in order to give the number per 
cubic meter of water. 
Distribution of plankton organisms . — ^The vertical distribution of the various plankton 
organisms in the five lakes on which pump catches were made is shown in the accom- 
T 
zzz 
Z2.\. 
21,8 
206 
t9.7 
15 2 
130 
1 1 2 
93 
05 
©2 
aa' 
Fig. 19 . — Vertical distribution of plankton organisms in Canadice Lake, Aug. 24 , 1910 . Scale, i vertical space=i meter; i 
horizontal space=s cnistacea, nauplii, and rotifers, and 100 algae and diatoms per liter of water. Predominant forms: 
Cyclops, Diaptomus, Ceraiium, and Asterionella. The column at the right marked O shows the quantity of dissolved 
oxygen at the various depths as indicated, and T represents the temperature. 
panying diagrams (fig. 19-23). These figures show the usual distribution of the 
chlorophyl-bearing portion of the plankton. That is, such organisms are confined 
chiefly to the epilimnion, where light conditions are most favorable for their photosyn- 
thetic activities. So much of the sun’s energy is absorbed by the upper meters of water 
that only a very small portion generally penetrates as far as the thermocline and the 
hypolimnion, thus making these regions unfavorable for the forms which depend upon 
light for the manufacture of an important element of their food. But in some of the 
small lakes of Wisconsin, which are well protected from wind, the top of the thermocline 
lies at such a slight depth — only 3 to 4 meters below the surface — that enough light for 
the process of photosynthesis reaches this stratum. This is shown by the large excess 
of oxygen that is sometimes found in this layer. 
