THE SALMON FAMILY 181 
migratory trout are coloured, spotted, and barred exactly like 
the young of lake and river trout, and in shape they are so 
closely similar as to require a long apprenticeship to enable one 
to tell them apart. Even experts cannot always agree about 
the species of these finger-marked salmonoids; in fact, the 
evidence about “‘ orange-fins ” of the Tweed, known as “ yellow- 
fins’ in the Solway rivers, is so conflicting that magistrates have 
refused repeatedly to punish persons convicted of killing them. 
Some witnesses declare them to be the young of migratory 
trout ; others pronounce them with equal confidence to be the 
young of river-trout ; while those of a third school are ready 
to swear that they are a distinct adult species. 
The juvenile dark bars, finger-marks, or “ parr-markings ” 
disappear in the migratory series upon their first descent to the 
sea, and are seen no more. So also do they disappear in 
such brook or lake trout as abundance of food enables to 
develop to a large size. But where food is scarce or water 
scanty, or where trout multiply unchecked beyond the natural 
resources of a lake, the fish never attain what may be reckoned 
the average size of their species; they are stunted in growth, 
and retain the finger-marks throughout life. This tends to the 
conclusion that these markings were part of the normal livery 
of primitive trout ; the inference being that, at no very distant 
date, all salmon, trout, and char were comprised in a single 
species ; that the more vigorous members of the race acquired 
by degrees the habit of resorting to the sea for food which the 
fresh water could not supply in sufficient quantity ; and that 
their changed habits and exposure to the vicissitudes of 
migration produced such permanent organic changes as 
differentiate the species. In many respects the subject remains 
very obscure; for example, it is not apparent why, if the 
explanation offered above is the true one, there should be 
different species of migratory salmonoid fish frequenting the 
same river. If these are all descended from common ancestors 
—trout—why are they not all true salmon, or salmon-trout, or 
