194 SOME MINOR PROBLEMS CONCERNED IN THE LOCAL
personal knowledge, extending back sixty years. The only variable
quantities appear to be the eel and stickleback, and these are easily
accounted for. The eel will sometimes leave the water and travel
from one pond to another, even across a gravel road. The stickle-
back, although not so shown in the table, is the most ubiquitous of
all our pond fish; but it must be remembered that it has often a
water communication denied to larger species. It will live in very
shallow ditches, which here, for the last half century at least, have
been effective barriers against other fish.
In this brief notice of the aquatic molluscs and the fish, the
element of temperature or still water seems to play an important part
in the distribution, for, however well the fish may be capable of