AUTHOR'S ABSTRACT OF THIS PAPER ISSUED BY 

 THE BIBLIOGRAPHIC SERVICE, MARCH l6, IQ2I. 



OBSERVATIONS ON THE LARV^ OF CORETHRA 

 PUNCTIPENNIS SAY. 



CHANCEY JUDAY.i 



INTRODUCTION. 



As part of a general problem relating to the biological produc- 

 tivity of lakes, a quantitative survey of the bottom fauna in the 

 deeper portions of Lake Mendota at Madison, Wisconsin, was 

 made between the early part of May, 1916, and the middle of 

 August, 1918. This survey included only the macroscopic forms, 

 such as the insect larvae, the Oligochseta, and the Mollusca. The 

 investigation showed that the full-grown larvae of Corethra punc- 

 tipcnnis Say constitute the principal element of the bottom popu- 

 lation in the daytime during the greater part of the year. For at 

 least three quarters of the year, in fact, they not only far outnum- 

 ber all of the other forms combined, but they also exceed them in 

 total weight. The great abundance of these larvae thus makes 

 them a very important factor in the biological complex of the 

 lake. 



Samples of the bottom were obtained by means of a modified 

 form of the Ekman dredge ; the opening of this instrument cov- 

 ered an area of 473 square centimeters. The mud obtained in 

 each haul of the dredge was washed through a gauze net having 

 meshes fine enough to retain all of the macroscopic forms. The 

 material secured by the net was transferred to a jar and was then 

 taken to the laboratory where the various organisms were sorted 

 out and enumerated in the living state. The average live and 

 dry weights of the various forms were also obtained, as well as 

 the percentage of ash. 



Observations were made at five regular stations located in 

 water having a depth of 20.5 meters to 23.5 meters. These sta- 

 tions were widely separated in order to secure a fair average of 

 the density of the bottom population in the deeper portions of the 



1 Notes from the Biological Laboratory of the Wisconsin Geological and 

 Natural History Survey No. XXI. 



2JI 



