Land and Fresh-Water Crustacea around Edinburgh. 49 
birds. And that this is probably the true means, appears 
from the fact that, the char-house being idle, birds have all 
freedom to alight undisturbed in and about the tanks. I 
have frequently seen starlings, wagtails, and house-sparrows, 
and sometimes a robin redbreast, sitting on the sides of the 
tanks.” Such is Mr MacLean’s account of this interesting 
example of the apparently erratic distribution of these 
Ostracods. 
In case it may be thought that the Ostracods were 
descended from those that may have been introduced before 
the supply of the Loch Thom water was shut off, I should, 
perhaps, add this further explanation. The only water that 
could get into the tanks, during the lengthened period they 
were not in use, was, as stated by my correspondent, supplied 
from the clouds, and, though that supply is sometimes con- 
siderable, it was seldom allowed to collect in any quantity. 
The uncovered tanks were separated from each other by a 
partition formed of iron plates; one of the tanks had an 
outlet pipe flush with the bottom, so that when necessary ail 
the water from that tank could be run off; the second tank 
- communicated with the first by a round hole through the 
iron partition, at about three or four inches from the bottom. 
In the one tank, therefore, all the water drained off as it fell, 
while, in the other, not more than a depth of three or four 
inches could collect, unless the hole in the iron partition 
was closed, which was rarely done. Being continually 
exposed to the sun and air, both tanks were consequently 
dry during a considerable part of the summer, unless the 
season were unusually wet. Mud, consisting of dust, blown 
by the wind, and of carbonaceous matter from the chimneys, 
collected in the bottoms of the tanks, but it was never allowed 
to accumulate, though the tanks were not in use; as a matter 
of fact, the tanks had been cleaned out, at least, twice since 
the time when the Loch Thom water was shut off, and before 
Ostracods were discovered. When the tanks were cleaned, 
the rust was carefully chipped or scraped off the cast-iron 
sides, which were then coated with tar, and the bottoms were 
swept with a brush; it is, therefore, hardly possible that 
the Ostracods observed could have been descendants from 
any that may have been introduced with the Loch Thom 
VOL. XIL. D 
