16 
quantitative collection from this body of water. As it was 
necessary to reduce the amount of field work, it seemed best for 
these reasons to drop this station permanently from the list of 
places subject to regular visitation. During the summer of 
1898, plankton collections have been made from time to time 
at the mouth of Flag Lake Slough in the hope of finding here 
Trochosphera, as‘in former years. None, however, could be 
found in this locality or, indeed, in any other in our field of 
operations during the past summer. 
As a rule, the collections made at the plankton stations 
above enumerated included a vertical one, one from the surface, 
and one from the bottom water, all made with a pump and a 
net of No. 20 silk bolting cloth. In addition to these a catch 
from a liter of water from a vertical sample at each station was 
made with filter paper, and from five liters with the Berkefeld 
filter, the first method of filtration being introduced in September, 
1896, and the second in November, 1897. The total number 
of bottles in the regular series for the years 1897 and 1898, 
each representing a different catch, is 1075. 
The collections above mentioned belong to the chronolog- 
ical series whose purpose is to afford a quantitative and qualita- 
tive representation of the changes through which the life in the 
water of the streams and the lakes examined passes during the 
course of a term of years. In addition to this series a con- 
siderable number of other catches have been made with a view 
to securing data upon certain allied and important phases of 
the plankton work. 
_ The relation of the dissolved gases of the water to the 
amount and constitution of the life therein contained is an im- 
portant problem, and an attempt to collect data has been made 
in connection with the Chemical Survey of the Waters of the 
State. In July, 1897, Prof. A. W. Palmer, Director of this 
Survey, visited the Station and made a number of analyses of 
the oxygen dissolved in the surface and bottom waters in the 
lakes and river. In 1898 his visit was repeated, with Mr. R. 
W. Stark, Assistant on the Survey, and a number of similar 
analyses were made, the carbon dioxide being also determined. 
A series of collections extending throughout twenty-four hours 
was made from the surface and bottom waters of the Illinois 
