2 Distribution of the Smaller Crustacea. [Sess. 
rence of certain species off the Scottish coasts which seem to 
owe their presence there to the influence of oceanic currents. 
And, third, a number of species—chiefly parasitic—will be 
referred to, the distribution of which appears, so far, to be 
inexplicable. 
First, The influence of the seasons on the distribution of 
the smaller crustacea. Though the changes of the seasons 
have, no doubt, a certain influence on the distribution of the 
smaller crustacean species, it is not always easy to ascertain, 
even approximately, how far this influence may be exerted, 
or to what extent the ordinary seasonal influences may be 
neutralised by changes that are accidental and temporary. 
Only by continuous observations extending over a number 
of years can any satisfactory knowledge concerning the influ- 
ence of the seasons on distribution be acquired. But though 
such a study may be difficult, and the results sometimes dis- 
appointing, it is nevertheless full of interest; and one of the 
reasons which make it unusually interesting is due to the 
unlooked-for incidents which are to be met with occasionally. 
I have stated that the ordinary seasonal influences may be 
interfered with by accidental and temporary changes: the 
following example will show how this may occur. The 
various species of Daphnia are, under ordinary circumstances, 
not greatly affected by seasonal changes. I have found them 
in Duddingston Loch, Loch Leven (Kinross), Forfar Loch, 
and other lochs which I have visited at various seasons, to 
be nearly, though not quite, as numerous in winter as in 
summer. (See Part III. of the 16th Annual Report of the 
Fishery Board for Scotland, p. 132 e¢ seg.) But though the 
distribution of Daphnia in these lochs did not appear to be 
ereatly affected by seasonal changes, it was otherwise with 
those observed in an artificial pond near Comely Bank, Edin- 
burgh. I visited this pond, with a friend, on July 3, 1898, 
and found Daphnia pulex abundant; on the 25th of the 
following month, or a little more than seven weeks after 
the first visit, I examined the pond a second time: the 
weather in the interval had been dry and warm, so that there 
was less water in the pond than at the first visit. Under 
