520 Peck u. Harrington, Plankton des Pnget-Sound. 



granular silt etc. This last named detritus (sometimes called ,,amor- 

 phous matter") is indeed one of the hardest elements to understand. 

 It is, to be sure, not strictly speaking a part of the Plankton, and 

 yet it constantly gives character to every sample of water, and often 

 outnumbers by many times the actually living material. It is most 

 varied in its appearance, from a light brown flocculent basis to finely 

 divided grit and sand. In this particular vertical the one -quarter 

 depth showed more of this debris than any other level, and as has 

 been seen this is correlated with a decrease in the quantity of living 

 plankton or the material derived immediately from it. The relation 

 of living organisms to detritus is not always constant, and for the 

 reason that the relation between them is so inconstant we believe 

 that it largely vitiates any volumetric estimate based upon merely the 

 bulk of a filtrate obtained from the water by net, planktonokrit or 

 filter. A sample may look, in gross, rich and promising, but on 

 examination prove almost barren of living plankton, although much 

 of the debris may be, more or less remotely, organic in origin. 



The observed numbers upon which this analysis rests may be 

 tabulated as follows: 



Under the item Coscinodiscm of the above table are seen certain 

 bracketed numbers at the right of the column. These denote the 

 dead individuals of that level, thus: Cos. occulus iridis has 19 at 

 surface level of which one (1) is dead. At the one -quarter depth 

 there are 22 of which twelve (12) are dead. At middepth there 

 are 32, of which eighteen (18) are dead, and so on for all the items 

 with following bracketed numbers. 



If now there be desired the numbers of these forms living in 

 each litre of ocean water in this region such a result may be obtained 

 by multiplying any of the above items by 50, since the organic filtrate 

 from the 1000 cc of water from each level is lodged in 20 cc of the 

 formalin preservative, while the above figures are taken from the 

 counting of 1 cc of such filtrate, or l/50 th part of the whole litre of 

 ocean water treated, at each level. 



It is not to be assumed, of course, that this reduces the analysis 

 of the contents of the water to a mathematical basis, as it only fur- 



