122 Bulletin Wisconsin Natural History Society [Vol. 13, No. 2 
tained at all times of the year. Merrill Springs (also called Minni- 
wakan Springs) and Merrill Creek — the latter a separate body 
of water, but fed by springs — have a constant temperature of 
about 10.0° to 11.5° centigrade ( = 50 — 53° Fahrenheit) throughout 
the year. 
The larvae of Diamesa mendota are found between the stones 
in the rapids of Merrill -Creek and the outlet* of Merrill Springs 
where the water flows fastest. For some reason they are much 
less numerous in the springs outlet than in the creek. It ap- 
pears that the optimum conditions are reached in the rapids of 
the creek. Since the temperature of the two bodies of water 
is practically alike, and alike throughout the year, temperature 
can hardly be said to be the decisive factor. The difference may 
be due to some chemical agent, as yet unknown to the writer. 
That there is some difference is indicated by the total absence of 
May-fly nymphs from the one, certain planarians and Trichop- 
tera from the other of the two bodies. A more detailed dis- 
cussion of the habitats is reserved for some other occasion. 
In the nymph the presence of gills and the form of the labium, 
in the pupa the number of anal filaments and type of armature, 
and in the adult the genitals of the male will serve to distinguish 
D. mendotae from its relatives. 
LITERATURE 
Johannsen, O. A. 1903 Aquatic Nematocerous Diptera. Bull. 68, N. Y. 
State Mus., pp. 288-327. 
1905 Aquatic Nematocerous Diptera II. Bull. 86, N*. Y. State 
Mus., pp. 76-315. 
Thienemann, A. 1908 Chironomidenmetamorphosen. Zeitschr. f. Wiss. 
Insektenbiol., 4, pp. 124-128, et al.,(p.l26, Diamesa insignipes). 
Zoological Laboratory 
University of Wisconsin. • 
January 31, 1915. 
