566 Wisconsin Academy of Sciences , Arts , and Letters. 
LIMNOLOGICAL APPARATUS 
BY GHANCEY JUDAY 
Notes from the Laboratory of the Wisconsin Geological 
and Natural History Survey. IX. 
The following paper was prepared in response to a num¬ 
ber of inquiries concerning limnological apparatus that have 
been received during the past few years. The first question 
that confronts the student who wishes to undertake a study 
of the biological problems presented by lakes is that of ob¬ 
taining suitable apparatus for such investigations. This 
question is not always an easy one to solve since much of 
the apparatus can not be purchased in the market but must 
be especially constructed. This means that designs must 
be prepared for the various instruments desired and a me¬ 
chanician employed to make them. 
A few of the standard types of apparatus are here de¬ 
scribed and illustrated with the hope that it may contribute 
to the solution of some of these preliminary difficulties and 
thus aid in arousing a more general interest in work of this 
character. 
PLANKTON NETS. 
Three types of net have been designed to meet the re¬ 
quirements of the various studies that have been made on 
the plankton. One of them is a small net, shown in Plate 
XXXVI, fig. 1, which is used in making the regular plankton 
catches for studying the number and vertical distribution 
of the organisms. It is used where only a comparatively 
small quantity of water, 10 liters to 50 liters, is strained. 
The second type is a larger net, shown in Plate XXXVI, fig. 1, 
which is used when larger quantities of water, 1,000 liters 
or more, are strained. The third type is a simple closing 
