FINGER LAKES OF NEW YORK. 239 



and that a more extended series of observations might have yielded somewhat different 

 results. The data in hand, however, are sufficient for a fairly good estimate. No 

 organisms were weighed in 19 10, but for purposes of comparison the data obtained in 

 19 1 8 have been applied to the numerical results of the former year. 



In 1910 Canandaigua Lake possessed the largest amount of crustacean material, 

 having about 2,579 kg./km.^ of surface, while Seneca Lake was second with slightly 

 more than three-quarters of this amount. Cayuga Lake, however, was less than 10 per 

 cent below Seneca Lake. The greater portion of the material consisted of copepods 

 in Canandaigua and Seneca Lakes; in the former they comprised about 67 per cent of 

 the total amount of crustacean material and in the latter about 79 per cent. 



In Cayuga Lake, however, about 72 per cent of the material consisted of the clado- 

 ceran Bosmina. Of the cladoceran material in Canandaigua Lake in 1910, Daphnia 

 retrocurva furnished about 30 times as much as Bosmina and about 4 times as much as 

 Diaphanosoma. Bosmina was the only representative of this group that was obtained 

 from the other two Finger Lakes in 19 10. Among the copepods Diaptomus was the 

 most important form in this year and Cyclops ranked second. 



In 191 8 Canandaigua Lake possessed only about a third as much crustacean material 

 as in 1910 and Cayuga Lake only about four-fifths as much. Seneca Lake, on the other 

 hand, showed a much larger amount in the former year, the amount exceeding that of 

 the latter year by about 62 per cent. Thus Seneca Lake in 1918 had almost four times 

 as much crustacean material as Canandaigua Lake and more than twice as much as 

 Cayuga Lake. Daphnia retrocurva was again the chief cladoceran element in Canan- 

 daigua Lake, but it was greatly exceeded by Bosmina in the other two lakes. Diaptomus 

 furnished the largest amount of crustacean material in Canandaigua and Cayuga Lakes, 

 but Cyclops was the chief constituent in Seneca Lake. 



Green Lake, Wis., possessed a larger amoimt of crustacean material in 19 18 than 

 was found in the three Finger Lakes either in 1918 or in 1910. It was almost 10 per 

 cent greater than that of Seneca Lake in 1918, which was the maximum for the three 

 Finger Lakes. The copepods formed a much larger proportion of the material in Green 

 Lake than in the Finger Lakes, because the Cladocera constituted a little less than 3 

 per cent of the total in this lake. Nearly two-thirds of the entire amount of crustacean 

 material in Green Lake was furnished by Diaptomus. 



Table 19 shows that the ash constitutes from 13 to 19 per cent of the dry weight 

 of the Crustacea of the Finger Lakes. In addition, also, it has been found that plankton 

 Crustacea contain from 4 to 9 per cent of chitin, which has no food value. In roimd 

 numbers, then, it may be said that about 20 per cent of the dry weight of the plankton 

 Crustacea from the Finger Lakes consists of ash and chitin, while about 80 per cent 

 may be regarded as actual food material. In the living state from 85 to 90 per cent 

 of the mass of these organisms consists of water, so that the live weight would be ap- 

 proximately 10 times as large as the figmes given in the dry weight column of Table 

 20, page 248. 



In the Crustacea from Green Lake the ash was much smaller, averaging somewhat 

 less than 6 per cent; adding to this about 6 per cent for chitin leaves about 88 per cent 

 of food material. The latter figure is higher than that for the Finger Lakes, which 

 is due to the higher percentage of ash in the material from these lakes. 



