Muttkowski—The Fauna of Lake Mendota. 437 
and the first damselfiies. Since pupal and adult stages of the 
various species overlap, and since many of them have a very 
brief pupal stage, I shall refer to these explicitly. 
In late June and early July the Ceratopogonine larvae pupate 
and after two to four days appear as adults. The case-building 
caddisworms which have pupated during late May and June 
leave their cases about the same time and appear as adults, be¬ 
ing conspicuous for a few days. In the latter half of the month 
the Hydroptilid caddisworms emerge after a brief week of pupal 
life. The larvae of Psephenus lecontei go to shore to pupate 
and their adults emerge in the early part of August. Simul¬ 
taneously with their emergence, the pupal life of Stenelmis 
crenatus is begun, lasting for about ten days, Dikerogam- 
marus for some reason is quite conspicuous at this time, while 
the young Hyalellae (fertilization takes place in late June) ap¬ 
pear to dominate for a brief period. 
All of these may in a way be said to prepare for the great cli¬ 
max of late August and early September. The eggs of caddis- 
fiies which were laid in early and middle July hatch at once (I 
exclude those of the Hydroptilids which do not hatch until the 
following year) and grow in quick stages. It seems little more 
than a month before the caddisworms have attained their full 
size. Hence by late August practically all of them are full 
grown. 
Now, this maturity is practically synchronous with the num¬ 
erical culmination of the small Oligochaeta and the greatest 
proliferation of plant life. To the student it seems as though 
the caddisworms and Oligochaeta received a sudden impetus 
which carried them to a rapid climax. This climax is indeed a 
remarkable one. Every plant, each leafiet, the bottoms of the 
plant zone, all will be found covered copiously with caddis¬ 
worms,—especially with Leptocella uwarowii and Helicopsyche 
borealis,—and with small Oligochaeta. But while the Trichop- 
tera appear greater in bulk, the small Oligochaeta outnumber 
them a thousand times, although they seem less in mass by rea¬ 
son of their transparency and their smaller size. So great is 
this multiplication of the Oligochaeta that they cover the leaves 
and stems of some plants like an animate scum. 
This ascendancy is paralleled to a lesser extent in other 
groups. Hydra proliferates in enormous numbers, but seems 
to attain its climax somewhat later in the season. Planarians, 
