272 
sults in large part, doubtless, from the greater number of 
catches averaged, and from the fact that they represent a num- 
ber of more widely separated points in a larger body of water, 
DISTRIBUTION OF PLANKTON IN LAKE ST, CLAIR. 
Plankton per sq. m. of surface 
Plankton per m.° of water 
Heel ean: Volume in Departure from} Volumein {Departure from 
; cm.® mean in per ct. cm.* mean in per ct. 
IlQ 5.00 7.19 —29.4 1.44 —55-4 
II 5.00 13.38 +31.3 2.68 —17.0 
IIIQ 5.54 15.27 ‘+49.9 2.76 —14.6 
Ill 5.54 21.55 111.5 3.89 +20.4 
IVQ 2.50 5.02 —50.7 2.01 —37.8 
IV 2.50 5.02 —50.7 2.01 —37.8 
VQ 5.26 14.40 +41.2 2.74 The 
V 5.26 19.04 +86.8 3.62 +12.1 
VIQ 4.70 10.93 +7.2 2,29 —29.1 
vi 4.70 14.69 +44.2 3.08 —4.7 
VIlQ 1.17 4.32 —57.5 3.69 +14.2 
Vil 1.17 4.32 —57.5 3.69 +14.2 
VIIIQ 4.44 II.99 +17.1 270 —16.4 
Vill 4.44 13.36 31.1 3.01 —6.8 
IXQ 4.28 10.88 +6.8 2.54 —21.3 
IX 4.28 10.22 +0.3 2.39 —26.0 
XQ 1.50 6:23 —38.8 4.15 +28 .5 
xX 1.50 6.23 —38.8 4.15 +28.5 
XIIIQ 2.21 10.59 +3.9 4.79 +48 .3 
XIll 2.21 8.76 —14.0 3.97 +22.9 
XIVQ 2.89 10.41 +2.2 3.60 +11.4 
XIV 2.89 9.56 —6.2 3.31 +2.5 
XVQ 5-17 9.29 —8.8 1.80 —44.2 
XV 5-17 12.50 +22.6 2.42 —25.1 
XVIQ 4.55 8.65 —I5.1 1.90 —41.2 
XVI 4.55 10.61 +4.1 2.33 —27.8 
XVIIIQ 1.27 7.09 —30.4 5.58 +72.8 
XVIIIQ, | 1.27 6.13 —39.8 4.83 +49.5 
XVIII 1.27 7.85 —22.9 6.18 +91.3 
Av. 10.19 +31.8 3.23 +28.8 
Range +I11.5 to —57.5 +o91.3 to —55.4 
in which currents, vegetation, shore, and bottom are important 
factors environing its plankton. 
This large variation in the distribution of the plankton in 
lakes naturally raises the question whether there is in the 
channel of a running stream, for example the Illinois River, a 
plankton whose uniformity of distribution is such that a collec- 
tion made ata given place and time may be considered as a fair 
