ANALYSIS OF ORGANISMS 173 



samples. The percentage of ether extract is smaller in Hyalella than in 

 the five samples of copepods, while the crude fiber and the nitrogen free 

 extract are larger in two of the latter samples. The percentage of ash 

 in the Hyalella material is from four to seven times as large as that in 

 these five samples of copepods. 



Including the ash, only two of the fourteen samples of Cladocera 

 yielded a smaller percentage of nitrogen than this sample of Hyalella, 

 but on an ash free basis only three of the former samples exceeded the 

 percentage of nitrogen in the latter. Including the ash seven samples 

 of Cladocera contained a larger percentage of ether extract than Hy- 

 alella, but this number is reduced to five on an ash free basis. On the 

 basis of dry material nine samples of Cladocera gave a larger percent- 

 age of crude fiber and twelve a larger amount of nitrogen free extract 

 than Hyalella, but both of these numbers are reduced to eight on an 

 ash free basis. The sample of Hyalella yielded a larger percentage of 

 ash than those of the Cladocera. 



OUgochaeta. The bottom mud in the deeper portions of Lake Men- 

 dota is inhabited by worms belonging to the genera Limnodrilus and 

 Tubifex. Enough specimens of these two forms were secured to permit 

 the determination of the nitrogen and of the ash. The nitrogen in this 

 sample of Oligochaeta amounted to 7.76 per cent of the dry weight, 

 which is equivalent to 48.5 per cent of crude protein; on an ash free 

 basis these amounts become 8.1 per cent and 50.62 per cent respectively. 

 These percentages are substantially the same as those noted in Volvox 

 and in about half a dozen samples of plankton Crustacea. 



The percentage of ash is smaller in this sample of Oligochaeta than in 

 the various samples of plankton Crustacea with the exception of Limno- 

 calanus. 



Hirudinea. A sample consisting of 286 leeches was collected on 

 August 28, 1915, in Lake Mendota. The specimens varied in length 

 from about six centimeters to ten centimeters and they represented 

 three different species. These leeches yielded a larger percentage of 

 nitrogen than any other form given in table 49. With the ash included, 

 11.13 per cent of the dry weight of this sample consisted of nitrogen, or 

 69.56 per cent of crude protein; on an ash free basis these amounts 

 become 11.82 per cent and 73.88 per cent respectively. The ether 

 extract amounted to 11.33 per cent of the organic matter, so that the 

 crude protein and the ether extract together constituted 85.21 per cent 

 of the organic matter in the sample ; this large percentage is exceeded 

 only by that of the crude protein and ether extract in Limnocalanus, 

 which constituted 88.35 per cent of the organic matter in this copepod. 



The percentages of pentosans and crude fiber are very small in this 

 sample of leeches ; the ash is somewhat larger than that in the sample 



