Muttkowski—The Fauna of Lake Mendota. 451 
tially that of the lake shallows, chiefly Ephemeridae, Aeshiiidae, 
and Libellulidae. 
Again, the Yahara River, passing through the swamps on the 
north, of Lake Mendota, carries with it a great deal of sediment, 
which makes it murky in its middle portions. Through its own 
force it is able to keep its channel unobstructed to a depth of 
about 3 meters. In this murky part no vegetation and an ex¬ 
ceedingly scant fauna exist. But in the shallower portions on 
its side the fauna and flora are of the stream type, with an es¬ 
pecially large representation of caddis-worms (chiefly Setodes 
grandis), damselfly larvae, and Hyalellae. 
This relation shows that current, while of so great an influence 
in changing the complex of the fauna, nevertheless is not an 
absolutely decisive factor, but that photosynthesis may affect dis¬ 
tribution and makeup in the establishment of a different sub¬ 
stratum. To what extent the makeup of the plant substratum 
is able to affect the faunal composition is indicated by a com¬ 
parison of the Yahara River, as just described, and Pheasant 
Branch Creek. 
In the latter Lestes forcipatus and other Zgyoptera larvae 
abound. Hyalellae are few, Setodes grandis scarce, beetle lar¬ 
vae plentiful, Culicidae rare, Nymphula larvae numerous; while 
in the Yahara River these faunal proportions are exactly the 
converse. 
Ponds .—It is a curious circumstance, that to a considerable 
extent the fauna of Pheasant Branch Creek and Picnic Pond 
have much in common. But while Pheasant Branch Creek has 
a strong current. Picnic Pond is stagnant, being maintained by 
seepage from the lake. Lepidoptera larvae, beetle larvae of 
various kinds, except Cyrinidae, Chironomidae, Lestes, Sympet- 
rum, and Libellula basalis among Odonata, and other species, 
are common to both regions. As for differences, Corethra is 
common in the pond (recruited from the lake) ; so are Culicidae 
larvae, Dytiscidae, Cyphonidae, Tipulidae, Stratiomyidae, 
Ephydridae, and certain other forms which are more or less 
limited in their distribution. 
Again, Tenney Park contains a large lagoon and a small pond. 
The lagoon contains flowing water, supplied from the lake, and 
its fauna is that of a stream. But the pond, small as it is (10 m. 
diameter) is noted as a depository of toad eggs, and harbors sev¬ 
eral faunal forms which agree with those of Picnic Pond, while 
