174 PROF. W. A. HERDMAN ON THE DISTRIBUTION 
a pure sample of Diatoms—a “ monotonic phytoplankton.” Similarly, when 
the zooplankton is at its height in late summer (usually September) the same 
net may contain almost a pure gathering of Copepoda numbering some tens 
to hundreds of thousands of individuals (up to 214,000), and making up 
perhaps 999 out of every thousand organisms presenta “monotonic 
zooplankton." But we may still regard the gathering as a zooplankton if 
over 50 per cent. of the organisms are animals—on account of their greater 
bulk. 
Moreover, these very abundant Diatoms and Copepoda belong in each ease 
to very few species, so that one can select about half-a-dozen species of 
Copepoda which constitute by far the greater part of the summer zooplankton, 
and about the same number of Diatoms whieh similarly make up the bulk 
of the spring phytoplankton. These few species, belonging to these two 
very widely separated groups, thus come to be the most significant organisms 
~ 
Fra. 1.—“ Hensen,” “ Nansen,” * Funnel” and other plankton nets 
drying after use on the yacht. 
in relation to the annual metabolic cycle of our seas and the food-supply 
from our coastal fisheries, Consequently it is of both scientific and economic 
importance to obtain such data as seem possible from our long series of 
observations, extending over a decade, as to the occurrence of these dominant 
factors in the plankton. No doubt there are exceptional years with unusual 
occurrences which will have a disturbing effect, but the ten or eleven years’ 
results ought to give us an average of some value. 
We have endeavoured, in our work from the yacht, as the result of many 
experiments, to make use of a standard net in a constant manner so that the 
hauls should be approximately comparable. Our two horizontal tow-nets of 
fine-meshed miller’s silk (No. 20 and No. 9) measure 35 em. (about 14 inches) 
