436 Wisconsin Academy of Sciences, Arts, and Letters. 
Coincident or ' slightly before the appearance of the adult 
Sialids, Chironomus digitatus will emerge, followed shortly 
afterwards by C. tentans, plumosus, and lobiferus. A little 
later, about the time the eggs of Sialis hatch,—that is, in early 
June,—there begins the exodus of mayflies. Usually about 
the first week of June Ephemera varia emerges, followed at 
once by millions of Caenis diminuta, and in quick succession by 
Ecdyurus and Heptagenia. Before the middle of June their 
flights are past. 
In the lake shallows, that is, in the cut-offs behind the bars, 
the images of Enallagma, Ischnura, Nehallennia, some Libelluli- 
dae, and Chrysops are conspicuous. They may be seen flying 
up and down, mating and ovipositing. The leaves of Castalia 
especially will show large batches of eggs of the various Zygop- 
tera, Chrysops, and Donaciinae on the upper or under surfaces. 
So many species have been eliminated from the lake by this 
time that the remaining ones attain a temporary dominance. 
Thus, the encrusting sponges and Bryozoa are conspicuous in 
the rocky areas, while among Cladophora and Spirogyra mil¬ 
lions of the small Hydroptilids and the Ceratopogonine larvae 
will be found. For a fortnight the migration of young Ne¬ 
matodes, Gordius aquaticus and a pink Nematode, makes them 
quite conspicuous in all parts of the lake. Of other species 
Amnicola limosa is euryedaphic at this time, but seems to favor 
especially the breaker line where it gathers in clusters exceed¬ 
ing a thousand specimens per square meter. 
Summer Succession—Period of Multiplication and Growth .— 
With the disappearance of Cladophora there is an intense growth 
of spermatophytes. Various species of Potamogeton, but es¬ 
pecially P. amplifolius, Myriophyllum, Ceratophyllum, Vallis- 
neria, Najas, and Chara luxuriate and with their rise begins 
the tremendous ascendancy of Trichoptera and small Oli- 
gochaeta. 
When the temperature of the water reaches about 15°, there 
begins the long series of wave-like ‘^flights” of Corethra. 
These occur in pulses about ten days apart, and last throughout 
the summer until the middle of September. Their climax is 
reached about the middle of July. 
These Corethra flights initiate what may be termed the ^‘sum¬ 
mer succession,” in contradistinction to the ‘Wernal succes¬ 
sion” which ends with the appearance of the may-fly species 
