Juday—Quantitative Studies of Fauna in Lake Mendota. 485 
The results of the chemical analyses made on the larvae of Sialis 
are shown in table 10. Substantially 69 per cent, of the dry weight 
of these larvae consists of crude protein and ether extract (fat), 
while relatively small percentages of crude fiber (chitin) and ash 
were found. The total nitrogen amounted to 8.52 per cent, of the 
dry weight, of which 0.45 per cent, was derived from the crude 
fiber, or chitin. 
On the basis of the spring crop of Corethra larvae, the total 
quantity of dry material in the various forms shown for the inter¬ 
mediate zone in table 17 amounts to about 63 per cent, as much 
as is indicated for the deep-water zone in table 15. Allowing for 
two crops of Corethra larvae per annum, the total amount of dry 
material in the intermediate zone becomes 64.2 kilograms per hec¬ 
tare (57.3 pounds per acre) as compared with 125 kilograms per 
hectare (112 pounds per acre) in the deep-water area. The latter 
figures may be regarded as representing the annual crops of bot¬ 
tom fauna in these two zones on the assumption that the Corethra 
larvae produce twice the April crop each year and that the other 
forms produce yearly a quantity of material equivalent to the 
average crop found in this investigation. 
Literature 
1. Baker, Frank O. 
1916. The relation of mollusks to fish in Oneida Lake. N. Y. State 
Coll. For. Syracuse Univ. Tech. Pub. 4: 15^366. 
1918. The productivity of invertebrate fish food on the bottom of 
Oneida Lake. N. Y. State Coll. For. Syracuse Univ. Tech. 
Pub. 9: 11-233, 
2. Bradley, H. C. 
1910-11. Manganese of the tissues of lower animals. Jour. Biol. 
Chem. 8: 237-249. 
3. Ekman, S. 
1914. Die Bodenfauna des Vaettern. Internat. Rev. 6: 146-425. 
4. Muttkowski, R. A. 
1918. The fauna of Lake Mendota. Trans. Wis. Acad. Sci., Arts, 
and Lett., 19: 374-482. 
5. Petersen, C. G. J. 
1911. Valuation of the sea. I. Rept. Danish Biol. Sta. 20: 1-76. 
1913. Valuation of the sea. II. Rept. Danish Biol. Sta. 21: 1-68. 
1918. The sea bottom and its production of fish food. Rept. Dan¬ 
ish Biol. iSta. 25: 1-62. 
