238 BULLETIN OK THE BUREAU OF FISHERIES. 



In Canandaigua Lake the Copepoda were more numerous in 1910 than in 1918, 

 but the reverse was true of the other two lakes. 



The number of Diaptomus was larger in the upper strata of Green Lake than in 

 any of the Finger Lakes, but Cyclops reached a larger numbe* than in Seneca Lake 

 only in the o to 5 m. stratum. 



The Cladocera consisted of representatives of Sida, Diaphanosoma, Daphnia, 

 Ceriodaphnia, and Bosmina. Bosmina was the most abundant form, and it was present 

 in the water of Caynga and Seneca Lakes in much larger numbers than in Canandaigua 

 Lake. The maximum number obtained was 19,100 per cubic meter of water in the 

 10 to 15 m. stratum of Seneca Lake. The average number in the upper 15 m. of Cayuga 

 and Seneca Lakes was 12,770 and 11,200 individuals per cubic meter, respectively. 



Ceriodaphnia was found only in the 5 to 10 m. stratum of Cayuga Lake and Sida 

 only in the o to 5 m. stratum of this lake. Diaphanosoma was noted only in the o to 5 

 m. stratum of Canandaigua Lake. 



Daphnia retrocurva was obtained from the upper 30 m. of Canandaigua Lake, and 

 a few young of this species were present in the 5 to 15 m. stratum of Cayuga Lake and 

 in the 10 to 15 m. stratum of Seneca Lake. 



In Canandaigua and Cayuga Lakes Cladocera were more abundant in 1910 than 

 in 1918, while the reverse-was true of Seneca Lake. 



The Cladocera were more numerous in Green Lake than in Canandaigua Lake, but 

 they did not reach as large a number as in Cayuga and Seneca Lakes. 



The numerical data serve to give a reasonably accurate notion of the plankton popu- 

 lation of these lakes, but such data alone do not give an adequate idea of the relative 

 value of the various forms as a source of food for other organisms. When they are 

 combined with data relating to the weights of the different organisms their value is 

 very greatly enhanced. By means of small platinum crucibles and a sensitive assayer's 

 balance the weights of the more important crustacean constituents of the plankton 

 were obtained and the results of such determinations are Shown in Table 19. Such 

 data have also been secured for various constituents of the plankton of Wisconsin lakes 

 and where such results were not obtained for some of the forms from the Finger Lakes, 

 those from the former lakes have been used in computing the data shown in Table 20. 

 The dry weight was obtained for all of the material and the wet weight as well for 

 a few of the forms; after taking the dry weight the material was ignited in an electric 

 furnace for the purpose of ascertaining the percentages of organic and inorganic matter. 



In computing the data for Crustacea in Table 20 the number of Crustacea per cubic 

 meter of water in a stratum was multiplied by the volume of that stratum and the total 

 for the lake was ascertained by adding the numbers in the various strata. This total 

 multiplied by the weight of the particular organism under consideration gave the 

 amount of such material in the entire lake; this quantity divided by the surface area 

 of the lake gave the weight per unit area, which is expressed in the table in kilograms 

 and pounds per square kilometer and acre, respectively. 



The amount of material per unit of surface is larger in the deep water than in the 

 shallow water, but the sides of these lakes have such steep slopes that the results would 

 not be altered very materially by taking this fact into consideration. Also it must 

 be borne in mind that these figures are based upon a single set of catches in each lake 



