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an inch-and-a-half mesh, hung to fish eight feet; a forty-yard 
minnow seine of one-fourth-inch mesh, hung to fish five feet; 
a thirty-foot minnow seine, hung to fish four feet; a Baird seine 
of the same dimensions; and a trammel net thirty yards in 
length and five feet in depth. The additions to the equipment 
consist of two set nets, one of three-fourths-inch mesh and 
eighteen-inch hoops, the other of an inch-and-a-half mesh and 
four-foot hoops. Thirteen fish traps of quarter-inch galvanized 
wire netting were constructed especially for the work in deep 
water and in places where a minnow seine could not be used. 
They consist of a cylinder of netting ten inches in diameter, 
one end of which is closed by a circle of wood and the other by 
two successive funnels sloping inward, each with an opening 
three inches in diameter. For the capture of the smallest fish. 
the nets are covered with fine wire cloth, and their efficiency is 
also increased by the use of wings of the same material or of 
minnow netting. 
The plankton operations of the last two years have been 
carried on with increased regularity and greater attention to the . 
correction of possible sources of error. The number of stations 
subject to regular examination at the beginning of the period 
covered by this report was seven; viz., the Illinois River two 
and a half miles above Havana, Quiver Lake, Dogfish Lake, 
Thompson’s Lake, Flag Lake, Phelps Lake, and Spoon River, 
the latter having been added to the list in August, 1896. (See 
Plate I.) The Illinois River station was visited at intervals of 
one month until July, 1896, in which month a number of ex- 
aminations were made at frequent intervals during a remark- 
able development of a filamentous diatom, Melosira, in the 
plankton, and in correlation with gas analyses conducted by 
Professor Palmer. Weekly collections upon Tuesdays were 
begun August 3, 1896, and have since been maintained except 
when the condition of the ice or sickness necessitated a slight 
shifting of the day of collection. 
The station in Quiver Lake was visited during intervals of 
one month during the first half of 1897, but during the latter 
part of July and the months of August and September the inter- 
val was reduced to a week. In October fortnightly visits were 
commenced, and have since been maintained. In the summer 
