261 
without reference to, and in most cases prior to, the prepara- 
tion of tables and plots of seasonal distribution. Estimates 
made by others, not accustomed to judging the plankton, re- 
veal a wide divergence in percentages, and independent esti- 
mates which I have made of the same material on different oc- 
casions show some divergence, though, as a rule, quite within 
the probable error of plankton method. The silt estimation 
does not, I believe, essentially vitiate any of the conclusions 
drawn in this discussion of quantitative results, and in no way 
enters into the qualitative analysis. 
THE CLOGGING OF THE NET. 
The collections made with the silk net drawn from the 
bottom to the surface of the water in vertical or oblique hauls 
are all diminished in volume to some extent by the resistance 
of the silk to the rapid passage of the water. As a result of 
this, the net pushes aside some of the water in the column which 
it is supposed to traverse. As its meshes clog with the accu- 
mulating catch the amount pushed aside is increased progres- 
sively during the haul. The actual catch of the net is there- 
fore only a portion of the total contents of the column of water, 
whose length is that of the haul and diameter that of the 
mouth of the net. The volume of plankton actually present 
in this column can be computed if we can determine the factor 
of correction. Hensen (’87 and ’95) has sought by experiment 
with filtered water to determine the mathematical formula 
which will give this correction for a net of known silk and di- 
mensions drawn at given velocities. This factor he calls 
the “coefficient of the net.” Reighard (’94) attempted to de- 
termine the coefficient of his net by using a miniature model 
in water in which Lobelia seeds had been placed, but ultimately 
adopted the formula of Hensen. 
It was necessary that in our final computation of the volume 
of plankton we should make some correction in all catches of 
the drawn net for this loss due to the pushing aside of the 
water. Since our net was constructed after the Hensen-Apstein 
model it was possible to apply the mathematical method of 
