464 Wisconsin Academy of Sciences, Arts, and LettVrs. 
The opening of these containers is rectangular in outline, being 36 
centimeters long by 28 centimeters wide, and they are 30 centi¬ 
meters deep. The capacity is about double that of the large dredge. 
Two handles are fastened to the top of the buckets about five centi¬ 
meters on either side of the middle. These handles are movable 
and are bent so that, when open, they conform to the outline of the 
top of the bucket and do not obstruct the opening. Double handles 
are used in order to make the containers stable when they are being 
carried. 
The samples of mud were diluted with about an equal volume 
of water, and they were then washed through a gauze net with 
meshes fine enough to retain all of the macroscopic organisms. The 
material which was retained by the net was taken to the laboratory 
where the various forms were enumerated in the living state. 
In addition to the numerical work, specimens of the various bot¬ 
tom inhabitants were picked out and weighed, so that gravimetric 
data relating to this population were obtained also. Both the live 
and the oven dry weights were ascertained as well as the ash. 
Small platinum dishes and a sensitive assayer’s balance were used 
for these gravimetric determinations. Several weights of each 
form were taken in order to get a general average; these weights 
included various sizes of the different forms and also represented 
different seasons of the year. Such numerical and gravimetric re¬ 
sults enable one to make a reasonably good estimate of the produc¬ 
tiveness of the bottom with respect to the various forms. Petersen 
(5) was the first to use this method of ascertaining the productive¬ 
ness of the bottom, and he has obtained some very interesting re¬ 
sults for the waters along the coast of Denmark. 
A. The Third or Deep-Water Zone 
The bottom population of the third or deep-water zone of Lake 
Mendota will be considered first. This population consists of the 
representatives of three groups of animals, namely: (1) worms 
belonging to the genera Limnodrilus and Tubifex; (2) a bivalve 
inollusk, Pisidium idakoense Roper; and (3) the larvae of three 
Diptera, Corethra punctipennis Say, Chironomus tentans Fabri- 
cius, and Protenthes choreas Meigen. 
The bottom-dwelling organisms which occupy the area within 
the 20-meter contour line have a fairly stable environment in so 
far as the temperature and the substratum are concerned. The 
