50 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
but I only did so because of the season of the year I was dealing 
with—the herrmg and the mackerel form no exception to the — 
rule that the fishes upon which man’s food from the sea depends, 
are nourished in their young and even in some cases in their 
older stages also by the abundant swarms of copepoda of our 
summer seas. 
It is not too much, then, to say that the fishes that form 
our food depend for their existence in our seas upon the cope- 
poda, and these copepoda themselves feed upon diatoms, 
which also nourished the little fishes at a younger stage, and 
these diatoms derive their food from the carbon dioxide im 
the sea-water, the varymg amount of which, at different 
seasons, according to whether or not it is then being used in 
the production of microscopic plants, causes those changes 
in the alkalinity with which I started this cycle of events. It 
is phenomena such as these, some of them, as you can imagine, 
of far-reaching importance, that are now being investigated 
by modern biologists—partly at our University laboratories, 
but partly also at such marine laboratories as our Port Erin 
Institution, in the foundation and progress of which, I may 
remind you, this Society has always taken a lively and helpful 
interest. 
