310 transactions liverpool biological society. 



Eestjlts. 



As there are four methods of estimation, naturally the 

 results may be conveniently grouped under four headings, 

 namely, results of volume estimation, weight estimation, 

 chemical analysis, and enumeration of the individual 

 constituents. 



The determination by volume has not been extensively 

 employed, so we proceed to the consideration of weight 

 estimation and chemical analysis, which had better be 

 taken together. 



Hensen (1) in his first work gives the results of fifteen 

 weight determinations. Three of these were of the whole 

 catch, which consisted mainly of Diatoms. Assuming 

 that the masses of these catches were contained in a body 

 of water of one square metre superficial area, and an 

 average depth of 20 metres, we find under a square metre 

 of surface in one case 1,608*3 ccm. of plankton, in another 

 2,72o ,, 5. The first mass contained 4*290 grams of dry 

 organic substance, the second 0*128 grams. These results 

 show very little dry organic substance, because the greater 

 quantity of the catch consisted of Diatoms, which not only 

 contain a large amount of water but on account of their 

 hard shells contain relatively more mineral than organic 

 substance. In 100 parts of dry substance, about 40 parts 

 would be organic and 00 parts ash. The Peridinese and 

 Copepoda gave a much smaller quantity of water and a 

 higher percentage of organic substance than the Diatoms. 

 For the Peridinese 100 parts of dry substance gave 90 

 parts organic to 4 parts ash. In the case of Copepoda the 

 percentage of organic substance was 99. Fresh, conse- 

 quently damp, Copepoda from the Baltic gave from 9 to 

 10 per cent, dry organic substance. The results are 

 interesting, as they show the large amount of organic 

 matter that the Copepoda contain, seeing that they form 



