275 
smaller number in waters of European lakes. For example, 
Apstein (’96) records 23 instances of hauls on the same date 
from equal depths and evidently in every case within distances 
between catches /ess than that represented in the extremes of 
our test. The number of hauls did not, however, in any of his 
tests eyzeed four. I have compiled or computed from Apstein’s 
table (pp. 56-57) the average and limits of departure from the 
mean in these 23 cases. In 12 of the 23 the average de- 
parture exceeds +3.58 per cent.—the average departure in 
our test, in which there were from two and a half to five times 
the number of hauls. In 10 of the 11 instances in which the 
departure from the mean in Apstein’s records falls below +3.58, 
only two hauls were averaged. The total range of the limits of 
departure also exceeds that found in our test in 8 of the 23 cases. 
In the light of Apstein’s results and considering the larger 
number of catches averaged in our test, and also the considera- 
ble length of the channel that it covers, it seems beyond rea- 
sonable doubt that single catches of the plankton inthe channel 
of the Illinois at our station of collection afford as trustworthy 
a basis for the analysis of plankton problems as do similar 
catches made in a lake. The margin of error thus introduced 
is no greater, if indeed so great, as that appearing in investiga- 
tions in such waters. 
Since these catches were made from an anchored boat, the 
water from which the plankton was taken was distributed over 
a considerable length of the stream. The test was made between 
7:30 and 9:30 a.m. The river stood at 5.1 ft. above low water 
and was falling rapidly, so that the current was noted at the 
time as unusually swift, probably approaching two miles an 
hour in mid-channel at this point. At this rate the collections 
represent plankton taken at ten intervals from a body of water 
about three miles in length. This areal distribution is compar- 
able with, if it does not exceed, the limits of widest distribu- 
tion of catches in Apstein’s tests, but it is much less than that 
of Reighard’s, which lay within an area of about ten by thirty 
miles. 
