476 Wisconsin Academy of Sciences, Arts, and Letters. 
the summer larvae average somewhat smaller than those of the 
winter generation, it may be conservatively estimated that the sum¬ 
mer broods are equal in weight to the winter generation. That is, 
the total annual production of Corethra larvae in this region of 
Lake Mendota may be estimated as about 1,200 kilograms of live 
material per hectare (a little over 1,000 pounds per acre), or some¬ 
what more than 100 kilograms of dry matter per hectare (about 90 
pounds per acre). These figures, however, apply only to that por¬ 
tion of Lake Mendota which lies within the 20-meter contour line, 
or to 16.8 per cent, of the total area. In the shallower water the 
larvae are found in much smaller numbers, as indicated on a sub¬ 
sequent page. 
The results of the chemical analyses of the larvae are shown in 
table 10. It will be noted that the percentage of nitrogen is espe¬ 
cially high, amounting to 10.7 per cent, of the dry material, and 
this means a correspondingly high percentage of crude protein, 
namely, a little more than 67 per cent, of the dry sample. The 
figure for nitrogen does not include that in the crude fiber or 
chitin, which amounted to 0.46 per cent, of the dry material; that 
is, the total nitrogen amounted to 11.2 per cent. The Corethra 
iarvae yielded a distinctly higher percentage of nitrogen than 
either the Oligochaeta or the larvae of Chironomus tentans, thus 
showing that they are a better source of nitrogenous material. 
The Corethra larvae also yielded a fairly large percentage of 
fat or ether extract. The crude protein and the fat together con¬ 
stituted more than 76 per cent, of the dry weight of these organ¬ 
isms. From the standpoint of quality, therefore, this large propor¬ 
tion of these two excellent food materials gives these larvae a very 
1 igh rank as a source of food for other forms. 
Protenthes choreus Meigen 
The larvae of Protenthes choreus were present in the mud of the 
deeper portion of the lake in comparatively small numbers. They 
were somewhat irregular in their distribution also, so that there 
were relatively large variations in numbers from time to time. The 
distribution by months is shown in table 13. There were marked 
differences in numbers during the winter, due mainly, perhaps, to 
the small number of observations made during this season. Seven¬ 
teen samples taken in April yielded an average of 400 Protenthes 
larvae per square meter, and 32 samples in May gave an average 
