276 Flow to obtain it. 
worthy of note, and that is that trout vary very much more in fresh 
water than they do in the salt. Some colours are also much more 
permanent than others. The experiment is now pretty well 
known of putting fish into a tank that is black and kept almost 
dark. When taken out and placed in the sunlight in a white 
bowl they look very black, but in a few minutes will often become 
light in colour. This is also largely the case with wild fish 
passing from lake to stream, or vice versa, or from one geological 
formation to another. Much more so is it the case when the 
_ Inigration is from river to sea, or sea to river; not only do the 
colours and general appearance of the fish become changed, but 
we find, in the case of fresh-water forms becoming anadromous, 
and vice versa, that the various organs and parts become altered’ 
also, probably by the law of adaptation. 
It is now an ascertained fact that trout (Sa/mo fario) can 
become anadromous in their habits. This seems to be largely 
the case in some of the rivers of New Zealand, and also in those 
of Tasmania. In British waters instances of brook trout migrat- 
ing to the sea are common enough. I have examined many 
brooks at low water, and have found beautiful little trout under 
the stones between tide marks. Quite possibly this may have an 
important bearing on the fine quality of the fish occurring in some 
lakes in close proximity to the sea, as, for instance, Loch Stennis, 
in Orkney. 
An interesting experiment was accidentally tried a few years 
ago by the owner of a fish pond near the sea. He built a rather 
elaborate outlet of heavy masonry, and carried it forward some 
distance into an estuary, so that the tide rose and fell within the 
walls. In it was placed a grating, which prevented fish passing in 
and out. Now it so happened that a few trout passed down out 
of the fresh-water pond above, and got into the tidal tank, which 
always had some two or three feet of water in it, and at high 
water a considerable depth. The water that entered from the sea 
usually swarmed with small crustaceans, etc., and when the trout 
were discovered some months afterwards they had grown to a 
much larger size than any in the large pond above, notwithstanding 
the confined area of the place in which they had been living. 
This opens up a very large question as to the future possibilities 
