655 
of Edinburgh, Session 1881-82. 
places, in short, where fishermen go to shoot their herring nets, 
guided by the presence of the birds and other animals. Here, 
within one or two fathoms of the surface, the tow-net gave only 
a few Copepods, Diatoms, and Echinoderm larvae. When, however, 
the tow-net was dragged at a depth of from 7 to 10 fathoms, 
it came up filled and covered with a mass of beautiful yellow 
or orange-coloured slime. This, on examination, was found to be 
composed of immense multitudes of Peridinium tripos. We may 
remark that none of these were in catena; whereas in the open 
ocean and more southern latitudes, these organisms are frequently 
met with in chains consisting of nine or ten individuals. Although 
these Peridinia are often regarded as flagellate infusorians, yet 
we could never detect either a flagellum or cilia, though we have 
observed them for several years. Indeed they seem to be undoubted 
algae, and their production in enormous abundance most probably 
depends on certain conditions of sunlight and temperature. Another 
haul of the tow-net at a depth exceeding 10 fathoms, gave vast numbers 
of the megalopa stage of crabs, together with a good many Cope- 
pods, Amphipods and larval fish. The stomachs of these Crustaceans 
were filled with Peridinia, so that these minute Algae supplied them 
with food. The herring and mackerel, which we procured from the 
fishermen, had their stomachs filled with these minute Crustaceans. 
The birds, again, were feeding upon the herring. Dolphins, whales, 
and dog fish were also busy upon the same ground, but, unfortunately 
we had no opportunity of examining their stomachs. 
We have here a chain of phenomena, which if carefully worked 
out, might give much information concerning the habits of many of 
our food fishes. The abundance of Peridinia gives food for the 
minute animals which are in a process of development in the ocean, 
and these again serve as food for our edible fishes. A knowledge of 
the food supply of these fishes, indeed, and of the conditions to which 
it is subject, would probably give the key to the solution of the 
mystery which at present surrounds the migrations of many of these 
fishes. That knowledge can best be acquired by a diligent and con- 
tinued use of the tow-net, together with an examination of the 
stomachs of the fish. In the stomach of the herring and mackerel 
which we examined during our cruises the following were 
observed : — Young of herring, sprat and other fish, Zoeas of crabs, 
