Dr. Charles A. Kofoid, the writer of the accompanying report on the plankton of 
the Illinois River, was appointed to the staff of the Illinois State Laboratory of Natural 
History as Superintendent of the Illinois Biological Station, July 1, 1895, and con- 
tinued in that relation until December 31, 1900. Elected Assistant Professor of 
Histology and Embryology in the University of California during the summer of the 
latter year, he received a virtual leave of absence from that University until the be- 
ginning of the January following to enable him to complete the collation and tabu- 
lation of the data of the Station studies, on which he was then engaged, and these 
materials were sent to him at Berkeley, California, early in 1901. His paper was 
thus mainly prepared after his formal connection with the State Laboratory had 
ceased, and during his residence in a distant state. 
Grateful acknowledgements are due to the University of California, and espe- 
cially to the successive heads of its Department of Zodlogy, Professor Joseph Le Conte 
and Professor William E. Ritter, for the privileges accorded in this connection. without 
which this report would necessarily have been prepared, under embarrassing disad- 
vantages, by another hand. 
S. A. FORBES, 
Director of Laboratory. 
Urbana, IIl., October 10, 1903.. 
