94 
BULLETIN or THE BUEEAU OF FISHERIES 
purpose by the United States Bureau of Fisheries. After it was found that there 
were usually no important variations observations were made only on certain 
occasions to indicate the influx of Gulf Stream and other ocean water. Had it 
been possible continuation of the daily tests would have been very desirable. 
Observations on the condition of the weather, sea, wind, and sky were taken 
daily. These factors are of great importance, particularly the winds, in determining 
the distribution of planktonic animals. 
Vertical hauls were made weekly, but they yielded rather disappointing residts. 
The water is only 11 feet deep at low tide, and for that reason a very small net of 
the Birge type, with a special bucket, was adopted. The material collected was 
centrifuged for two minutes at about 1,000 revolutions per minute in a graduated 
glass tube, and the result measured in cubic centimeters. The figures obtained 
are not included in this report because I did not have time to make individual 
counts of the various species, and the total mass was meaningless, being made 
up of diatoms, dinoflagellates, particles of dirt and detritus, larval copepods, larval 
mollusks, and an occasional adult copepod. All the large planktonic forms had 
successfully evaded the net as it was being drawn to the surface, and the resulting 
mass did not give a fair estimate of the amount of plankton in the water at the time. 
To get these various-sized animals, a series of nets of at least 10 different meshes 
would be necessary, and even with these there would be so much overlapping that 
the results would be of little value. The pump has not succeeded in overcoming 
this difficxilty in the case of the marine plankton. On eight occasions during the 
past year I centrifuged over 100 samples taken by pump in Long Island Sound, 
and invariably the deposit contained a larger proportion of small forms and a 
smaller proportion of large forms than did the vertical hauls made at the same 
time. A successful method of accurately determining the real volimie of marine 
zooplankton as well as of phytoplankton is yet to be devised. 
The most valuable results were obtained with surface nets. The waters are 
so churned up in Great Harbor that there was no difference in the collections taken 
at the surface and those taken at the bottom, except that the latter often contained 
more sand and small detritus. For that reason the bottom hauls were discontinued. 
The daily routine of plankton collecting and investigation, consisted of three 
parts. First, the nets were suspended from the end of the dock by means of pulleys 
attached to outlying piles in such a position that one was suspended in a northerly 
direction and the other in a southerly one (fig. 1, p. 97). 
Wlien the nets were hauled the contents were emptied into a flat glass dish 
entirely covered with black paint except for a small area at one comer. A tight- 
fitting top completely shut out all light except in the corner over the clear glass. 
A light placed at this end caused all the Crustacea, larval annelids, and, in fact, 
most of the free-swimming planktonic organisms that are positively phototropic 
to crowd at the lighted corner, where they cotdd be picked out individually with 
a pipette or drawn out in bunches with a long glass tube and deposited in a watch 
glass or petri dish for examination. A second collection was then made from the 
detritus in the bottom, consisting of dead organisms and any forms that had not 
been attracted to the light. Finally, the last bit of sediment, after all the rest of 
the tow had been poured into a sUk bag to be strained, was placed in a dish. This 
