4 
special breeding habits, variations in color, and the rate of 
growth of the different species at different times of the year. 
As an equipment for this work I provided a number of 
fish-traps and set-nets of uniform size and character, The 
traps were made of galvanized- wire cloth, in the form of a 
cylinder, about a foot in diameter and four feet long, one end 
being closed, and the other fitted with two funnels with the 
small ends pointing inward as in an ordinary fyke-net. The 
set of fyke-nets were such as are commonly used by Illinois 
fishermen and were made in two principal sizes; one, of quar- 
ter-inch mesh, with a body two feet in diameter and wings 
spreading about four feet, and the other, of two-inch mesh, 
with a body four feet across and the spread of the wings about 
eight feet. In connection with these nets a seine forty yards 
long and six feet deep, with a quarter-inch mesh, was fre- 
quently used. : 
With this apparatus, parallel catches of fish at a number 
of carefully chosen stations were made at regular intervals 
throughout the entire period, the fishes caught were identified, 
the specimens were counted for each species in each catch, 
and the data thus obtained were used as the materials of a 
statistical study of the varying occurrence of the species. 
This was practically an adaptation to ichthyology of the 
methods of the plankton biologist. ‘The whole product of the 
work has been tabulated and studied with a view to general 
results, and a paper on this subject by Mr. Craig will be in 
hand for publication some time this winter. Five of the sta- 
tions were in the Llinois River, one in Spoon River, and three 
in bottom-land lakes connected with the larger stream. In 
the Illinois the conditions vary with time and place, but the 
water is generally muddy, with moderate current. The Spoon 
River situation was far more variable than the Illinois, but 
generally the water was muddier and the current swifter. In 
the lakes, of course, the current is slight and the waters are 
much more clear. This application of the statistical method of 
study to ichthyology is already justified by the results of this 
first attempt, some of which may be thus briefly described:— 
The fishes of the Station field may be quite closely divided 
