1896 - 97 .] Mr George Murray on Marine Diatoms. 
211 
summer, so far as my observations went, from the west coast except 
in two places, viz., off Sheep Island near Oban, where it occurred 
sparingly, and in Loch Etive, where it occurred in almost as great 
abundance as in the Clyde in spring. I could find no local tempera- 
ture conditions to account for this — the only outstanding physical 
point of resemblance was the large quantity of fresh water on the 
surface of the Clyde in spring and in Loch Etive in August. 
Only in Loch Etive and in the Sound of Mull did I obtain hauls 
of diatoms in summer that were comparable in quantity with those 
obtained generally in the sea in spring. This seasonal occurrence 
may be connected, I venture to think, with another observation of 
economic interest. I discovered that the Copepoda and other 
minute Crustacea were living on the diatoms, both by direct 
observation and by examining their cylindrical lumps of ex- 
crement, which consisted entirely of diatom chromatophores (main- 
taining perfectly their characteristic shapes and even partly their 
hue) and of minute fragments of the siliceous frustules — both 
chromatophores and fragments of frustules being determinable as 
those of the diatoms in the same haul. I searched daily for three 
weeks in summer for similar evidence of their eating Ceratium , 
but in vain. This negative evidence, however, is not of much 
value, since the Peridinieoe , from their structure, would be less likely 
to leave traces after passage through the digestive tract. Every 
diatomist knows of the abundance of diatoms in the guano deposits 
of sea birds that presumably devoured fishes that in turn live on 
small Crustacea. Moreover, diatoms are frequently found in the 
stomachs of Holothurke, Ascidians, Salpse ; oysters, scallops, 
whelks, and other molluscs ; crab, lobster, and other large 
Crustacea, and even in those of full grown fishes. We have been 
able in the past to infer that diatoms and other pelagic algae formed 
the basis of the nutrition of all sea animals, — the pastures of the 
sea, — and I count myself fortunate to have been able to establish by 
direct observation this important link — that the small Crustacea, 
which themselves are so important a food of fishes, feed directly on 
diatoms. 
In order to determine whether diatoms are present to any extent 
in the digestive tract of young fishes, either from having been 
eaten directly by them or inside small Crustacea eaten by the fish, 
