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 



