Muttkowski—The Fauna of Lake Mendota. 
409 
forms the head of the larva is elongate, and the antennae are 
frequently retractile. The following forms have been found 
in the lake. 
Protenthes choreus Meigen. 
The distribution of this species is practically identical with 
that of Chironomus tentans in the lake. It is fairly abundant 
in the bottom mud and forms an important item of fish food. 
Tanypus decoloratus Malloch; Tanypus monilis Linne; Tanyp- 
us carneus Fabricius. 
These three species occur in the lake, but only T. monilis in 
appreciable numbers. All three are littoral forms. The lar¬ 
va of T. monilis is remarkable for its retrogressive locomotion, 
resembling that of a crayfish. None of the species build true 
cases, but live free or in concretions which are loosely put to¬ 
gether. 
Chironominae. 
This subfamily comprises the true ‘^blood-worms,” although 
this designation is somewhat of a misnomer. Most of the spe¬ 
cies are able to spin tubes, using plant fibers or sand granules. 
Chironomus abbreviatus Kieffer. 
This is species number 82 of Johannsen (1905). The species 
is littoral and sublittoral in its distribution. 
Chironomus tentans Fabricius. 
This is the largest of all Chironomid species that occur in the 
lake. Its distribution is practically confined to the bottom 
area of the lake, although it occurs in great numbers in the 
muddy areas behind the bars of University and Catfish bays. 
It is stenoedaphic in mud, hence limophilous. Larvae have 
been taken from the lake, ponds, creeks, in fact wherever a 
mud bottom occurs. 
The larvae are extensively parasitized by Gordius, at times 
by as many as three individuals, although usually only a single 
parasite is present in the larva or pupa. The species trans¬ 
forms during late April and May and late September and Oc¬ 
tober. There is a peculiar parallelism between transforma¬ 
tion and the amount of available oxygen, transformation de- 
