240 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
and lowered vertically at a uniform speed through a 
certain stratum of water. ‘The net is to be hauled up 
vertically, allowing no chance of horizontal towage, 
through the same stratum of water, the speed of haul 
being noted. The exact volume of water pumped up is, 
of course, known; the catch can be abstracted from this 
in two ways. First, if the comparison of volume caught 
is to be the basis of the coefficient, the water from the 
pump is filtered through a net of the same material as the 
net which is being examined, so that it may abstract 
approximately the same kind of catch as it would when 
pulled through the water. The net which is being used 
as filter must be floated on the surface of the water so 
that the filtering area is submerged, and some arrange- 
ment should be used to spread the water pumped into it, 
so that it does not hit one part with too great a force. 
This filtered catch is then fixed and centrifuged, in order 
to determine the volume. The catch made with the net 
is also fixed, centrifuged and the volume taken. Knowing 
now the volume of water which the filtered pump catch 
represents, it is easy to find how much water must have 
been filtered by the net to have given the volume of 
plankton caught by the latter. 
Another way would be to filter the water fiom the 
pump through hardened paper so that nothing but the 
smallest organisms would be lost, then to count, by the 
usual methods, some organisms in the catch which occur 
uniformly distributed in the area where the experiments 
are carried out, and which are caught accurately by both 
net and pump methods. Small forms which are lost by 
the net are therefore cut out, and even copepoda or 
metazoa which swim actively and generally are very 
sensitive to currents against which they move, may not 
