1897.] NEAV YORK ACADEMY OF SCIENCES. -385 



this water includes many bits of epidermis of plants, many of the 

 epidermal stellate hairs like those upon many ferns. There is 

 also the almost constant presence of wing scales from Lepidop- 

 tera, and back of all the blackish or brownish granular silt, etc. 

 This last named detritus (sometimes called " amorphous 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 

 constantl}' 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 lloht 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 immedi- 

 ately from it. This 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 volu- 

 metric estimates 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 proves al- 

 most barren of living plankton, although much of the debris may 

 be, more or less remotel}^, organic in origin. 



The observed numbers upon which this analysis rests may be 

 tabulated as follows : 



Under the item Coscinodiscus of the above table are seen cer- 

 tain bracketed numbers at the right of the column. These de- 

 note 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 numbers of these forms living in 

 ocean water in this region such a result may be obtained by mul- 

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



Transactions N. Y. Acad. Sci., Vol. XVI., Sig. 25, May 20, 1898. 



