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 

 Trochosphcera, 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 dift'erent catch, is 1075. 



The collections above mentioned belong to the chronolog- 

 ical series whose purpose is to aft'ord 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 tlie 

 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 wa3 repeated, witli Mr, P. 

 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 



