Peck u. Harrington, Plankton cles Pugot-Sound. 517 



individuals at that point, as likewise the width of the oblique -lined 

 belt shows the quantity of the dead and the broken tests of the same. 



From the data obtained by us, and represented by the plotting 

 on Fig. 2, it will now be seen that the dinoflagellate Peridinium 

 represented in the first column, is very abundant at the surface, also 

 that of the two species represented the one, P. fusus, is much more 

 numerous than the other, P. diveryens, the latter being only about 

 one -tenth as numerous as the former as is here represented by the 

 stippled portion on the right side of the column. At the one -quarter 

 depth (28 fathoms) the decrease in this organism is very marked, 

 while the falling off continues thence gradually to the bottom. It is 

 plain, however, that P. fusus can maintain itself alive at the bottom, 

 and that the larger species, P. divergens, shows a more uniform distri- 

 bution throughout the upper half of the vertical but runs rapidly out 

 in the lower half, being absent at the last two levels. 



The distribution of the diatoms included under the heading Cos- 

 einodiseus is much more varied as is shown in the second column of 

 the plate; taking all the elements together there is shown a uniform 

 increase from surface to middepth, then a rapid increase to the three- 

 quarters depth, with a final falling off in the last quarter distance of 

 the vertical. It will be seen, however, that there is a large element 

 of dead and broken debris here included (represented by the oblique- 

 lined sides of the column), which we assume to have settled from 

 surface strata, and which would thus naturally increase towards the 

 bottom. In the living and uninjured part of the material one sees the 

 same plan, except that the proportion of living to dead organisms is 

 much greater at the surface than at any other level. The living- 

 diatoms of this group are over 82/ of the whole number at surface, 

 as against 23/ at the three-quarter depth, and as against 29/ at 

 the bottom. 



It may be that some currents at superficial levels are at work in 

 shiftig off the material, so causing it to be settled or eddied into 

 belts and strata below, and it may be that there is also a higher 

 rate of disintegration in the bottom strata to account for the lessening 

 quantity there but this seems hardly possible within these short limits, 

 and we believe that this difference in quantity at different levels is 

 rather due to those circumstances which cause a sudden loss in the 

 rate of reproduction in the upper strata, and from which there is a 

 subsequent settling of the debris into the lower. As will appear upon 

 a following page the diatoms here considered are very variable in 

 quantity at the surface, being at some times very abundant and at 

 others (as on the day when this vertical was taken) hardly percep- 

 tible. From this it is certain that the column in black as here plotted 

 would on another day, during a period of rapid growth at the sur- 



