at which
time they were nine months old. In January 1841, they had increased to
three and a half inches, exhibiting a somewhat defective condition
during the winter months, in one or more of which, Mr Shaw seems to
think, they scarcely grow at all. We need not here go through the entire
detail of these experiments.[23] In October (twenty-one months) they
measured six inches in length, and had lost those lateral bars, or
transverse markings, which characterise the general family in their
early state. At this period they greatly resembled certain varieties of
the common river-trout, and the males had now attained the age of sexual
completion, although none of the females had matured the roe. This
physiological fact is also observable in the true salmon. In the month
of May, three-fourths of the brood (being now upwards of two years old,
and seven inches long) assumed the fine clear silvery lustre which
characterises the migratory condition, being thus converted into smolts,
closely resembling those of salmon in their general aspect, although
easily to be distinguished by the orange tips of the pectoral fins, and
other characters with which we shall not here afflict our readers.

[23] A complete series of specimens, from the day of hatching
till about the middle of the sixth year, has been deposited by
Mr Shaw in the Museum of the Royal Society of Edinburgh.

The natural economy of the sea-trout thus far approximates that of the
genuine salmon, but with the following exception. Mr Shaw is of opinion
that about one-fourth of each brood never assume the silvery lustre;
and, as they are never seen to migrate in a dusky state towards the sea,
he infers that a certain portion of the species may be permanent
residents in fresh water.[24] In this respect, then, they resemble the
river-trout, and afford an example of those numerous gradations, both of
form and instinct, which compose the harmonious chain of nature's
perfect kingdom. In support of this power of adaptation to fresh water
possessed by sea-trout, Mr Shaw refers to a statement by the late Dr
McCulloch, that these fish had become permanent inhabitants of a loch in
the island of Lismore, Argyllshire. Similar facts have been recorded by
other naturalists, though, upon the whole, in a somewhat vague and
inconclusive manner. We have it in our power to mention a very marked
example. When certain springs were conducted, about twenty years ago,
from the slopes of