478 Wisconsin Academy of Sciences, Arts, and Letters. 
While the larvae of Protenthes choreas are eaten extensively by 
fishes, they do not play nearly as important a role in the diet of 
these animals as the other two dipterous larvae found in the deeper 
water, because they average much smaller in size than the chiron- 
omid larvae and are also less abundant, and because they are pres¬ 
ent in very much smaller numbers than the larvae of Corethra. 
The gravimetric data for the various organisms inhabiting the 
bottom in the deeper water of Lake Mendota are summarized in 
table 15. For the live weights the totals do not include Pisidium 
idahoense because such data were not obtained for this form. The 
weights given for the larvae of Corethra show only the April crop, 
but, even on this basis, these larvae yield about four times as much 
dry material as the next form in importance, namely, Chironomus 
tentans. Just the April crop of Corethra larvae, in fact, contains 
more dry material than all the other forms combined. If the sum¬ 
mer broods of this form be added, it shows a very marked excess 
over the others. The larvae of Protenthes yielded the smallest 
amount of material. 
The annual production of the various forms has not been esti¬ 
mated except for the Corethra larvae. It would probably not be 
far from the actual production to assume that each of the other 
forms produces annually a quantity of material equivalent to the 
average amount found in this investigation, while Corethra yields 
twice as much as was noted for this form in April. On this basis, 
the total annual yield of these bottom forms within the area under 
consideration would amount to somewhat more than 1,255 kilo¬ 
grams per hectare live weight, including Pisidium (1,120 pounds 
per acre), or a dry weight of about 125 kilograms per hectare (112 
pounds per acre). The Corethra larvae are responsible for about 
77 per cent, of this quantity of dry material, and the larvae of 
Chironomus tentans for about 10 per cent., while Limnodrilus and 
Tubifex come third with somewhat less than 9 per cent. For the 
deep-water zone, which comprises 664 hectares, this would mean 
an annual crop of slightly more than 833 metric tons of these or¬ 
ganisms in the living state, or 83 metric tons of dry material. 
B. Station I 
In addition to the five stations located in the deep water, a 
sixth station was visited regularly. The latter is situated in the 
southern portion of the deeper water, between Picnic Point and 
