PLANKTON STUDIES ON LAKE MEND OTA. I. 



THE VERTICAL DISTRIBUTION OF THE PELAGIC 

 CRUSTACEA DURING JULY, 1894. 



E. A. BIRGE, 

 Professor of Zoology, University of Wisconsin, 



ASSISTKD BY 



o. a. olson and n. p. harder. 



INTRODUCTION. 



The following paper is the result of the joint work of Mr. 

 Mr. O. A. Olson and H. P. Harder, members of the class of 

 1895 of the University of Wisconsin, done under my direction, 

 and with my aid, for graduating theses in the College of Letters 

 and Science. The observations occupied about six weeks of the 

 summer of 1894. The first ten days, beginning about July 5, 

 1894, were spent in preliminary work, experimenting with the 

 dredge and with methods of counting. The last observations 

 were made on th** 4th of August, and the finishing of the 

 counting of specimens occupied about another week. Messrs. 

 Harder and Olson did most of the dredging, taking the observa- 

 tions, day and night, at regular intervals whenever the state of 

 the weather permitted. The observations at 6 and 9 p. m. were 

 ordinarily made by myself. The counting and the exceedingly 

 wearisome computation of percentages and averages was also 

 performed by them. In this latter work Mr. Olson was re- 

 sponsible for Cyclops and D. pulicaria, while Mr. Harder did 

 the computing for Diaptomus and D. hyalina. Each, however, 

 checked the work of the other, so that great accuracy has been 

 obtained, both in counting and in computation. Mr. Harder 

 was absent after the completion of the observations, while Mr. 

 Olson has been in attendance at the University and has 

 done much work during the college year. 



The results of the investigation were written up and reported 



