PLANKTON OF THE WOODS HOLE REGION 95 
was often found to contain large numbers of small mollusks, ostracods, and Foram- 
inifera. 
After the living specimens had been observed they were killed with a 2 per 
cent solution of formalin and reexamined. The species not readily identified were 
placed in separate watch glasses and subjected later to a more careful examination 
with a higher-power lens. For a general examination of zooplankton a binocular 
microscope with low-power lenses (Nos. 55, 40, and 24) is very satisfactory. Smaller 
forms were mounted on slides and examined with a compound microscope. 
Several samples of phytoplankton were placed in watch glasses and examined 
alive. This made possible a rapid survey of a large amount of material. Next 
some of the material was mounted on slides, with barium mercuric iodide as a mount- 
ing medium, and examined with a higher-power lens. 
The common species were tabulated daily on charts, records being made of 
the rarer specimens. If these began to appear frequently, they were given a place 
on the chart. This method proved to be very simple and convenient. The material 
was later put in 2 per cent formalin and labeled for future reference. 
The direction of the currents in Great Harbor during the flood tide 
(fig. 1, p. 97) was determined in two ways. The first method was very simple, 
consisting of observations made while great masses of broken ice were floating 
through the passage during the spring months. The results obtained in this way 
could be checked up as often as desired. The second method was used to determine 
the smaller currents near shore, and the course of the back eddy along the shore 
of Nonamesset. This was accomplished by placing large quantities of shavings in 
the water on a calm day and plotting the courses which they took. The resultsmay 
not be entirely accurate in minute details, but they show the general movements of 
the water in the harbor during flood tide. 
The combined results of my observations on material of 1899-1900 and those 
of Mr. Edwards have been plotted on quadrille paper. The charts based on the work 
of the past two years are on Keuffel and Esser No. 334D graph paper. 
A great difficulty presented itself when I started to assemble my results. In 
qualitative work the greatest amount of material possible is essential, and the 
only way to obtain this is by surface towing, which obviously does not lend itself 
to any accurate measurement. Hven if figures could be secured the daily variation 
in the winds and tides is so great at Woods Hole that the results would be more 
confusing than helpful. One can state when the first specimen of a species appears 
and when its season ends, and the fact that the numbers may be increasing daily 
can also be seen, but to present this information in a satisfactory manner is difficult. 
The plan finally adopted consisted of the use of four categories—very scarce, 
scarce, abundant, and very abundant. These served as calibrating points from 
which the seasonal distribution of a species could be plotted in a fairly accurate 
manner. Of course, the basis for measuring the abundance of copepods was not 
the same as that for the diatoms; 500 of the former might be considered abundant, 
while the same number of diatoms would be considered very scanty. Again, 50 
specimens of the oceanic annelid, Tomopterus, would be considered abundant, 
but 50 specimens of a common copepod would be thought scarce. The measure- 
ment, therefore, is relative; that is, the symbol given to a particular animal for a 
