NOTES ON FRESHWATER ENTOMOSTRACA 171 
have made a study of the little creatures. The cause that 
leads to such an exodus—it can scarcely be called destruction 
—taking place may not always be obvious, but in the 
majority of cases it is probably brought about by a sudden 
change of temperature, when the weather from being mild 
and warm becomes cold and ungenial, or when there 
happens to be a prolonged and intense cold such as has 
been experienced during the past winter. Under such 
conditions, free-swimming entomostraca—and it is only 
such that seem to be much affected—-appear to become 
temporarily enfeebled ; and those of them which happen to 
be in the neighbourhood of that part of the loch where the 
river takes its rise are thus less able to contend against the 
currents, which gradually increase in force the nearer the 
overflow or excess of water of the loch approaches the open- 
ing of the river, and so, being overpowered, are carried away 
with the stream. This is the more likely to take place in a 
loch where the water is comparatively shallow, as it will in 
that case be more readily influenced by atmospheric changes. 
I have records of several instances where entomostraca 
have been observed in unlooked-for places. At Rothesay, in 
the spring of 1887, these little “beasts ” occurred in consider- 
able numbers in the water supplied to the town for domestic 
purposes. They were collected by fixing a piece of thick 
flannel cloth on the water-tap; and after allowing the water 
to run through the cloth for an hour or two, it was taken off 
and washed in water in a glass tumbler—myriads of the 
creatures could then be seen swimming about in the water. 
In the spring of 1888 a friend sent me a number of ento- 
mostraca from Campbelltown that had been collected in the 
same way. Last year I happened to be at Barra during the 
month of May, and the weather for part of the time was cold 
and unpleasant. One day my attention was directed to the 
presence of numerous “beasts” in the water that was supplied 
for domestic use from a reservoir behind the village of 
Castlebay. These “beasts” proved to be Diaptomus serricornis 
and one or two Cyclops. “Beasts” that had been obtained 
in the water supplied to Edinburgh have likewise on one or 
two occasions been brought to me, and they also turned out 
to be ‘ water-fleas,—Cyclops viridis, if I remember right. It 
