134 SALMON AND TROUT. 
and February following, a few fish continue to run which 
have been usually considered as ‘barren ’—without capability 
of spawning; but this notion was proved by ‘the late Mr. 
W. F. Ffennell to be erroneous. Upon dissection he found 
that the females had ova in them perfectly developed, although 
not larger than mustard seed, whilst in the males a thin thread 
of milt was always discernible. 
These fish, of which many ascend the Tay in November 
and the three following months, remain nearly a year in the 
fresh waters before spawning, and although their colours gra- 
dually become darker in consequence, they are to all intents 
and purposes ‘clean fish,’ and are exceedingly good eating. 
The term ‘clean fish’ is used as the antithesis of ‘ foul fish’ 
—a term applied to all salmon which have either not recovered 
from the effects of spawning, or in which the roe or milt has 
arrived at a great degree of maturity. 
The so-called barren salmon appearing at a time when most 
fish are spawning, or are just recovering from the process, illus- 
trates what I believe to be the most important fact connected 
with the history of salmon, viz. that the principle of a divided 
migration, already referred to, is not confined to the parr on 
going to the sea, or to the smolts on their return from it, some 
as grilse, and some as spring salmon, but that it also extends to 
the old and adult fish after spawning—one portion of these 
latter coming back into the rivers during the following summer, 
and the rest not until the spring succeeding it ; in other words 
(and this is the gist of the whole), that at least a proportion of 
salmon spawn only every alternate year. The design of this law 
or instinct—which, when once apprehended, will be found to 
explain many of the perplexities in the history of the salmon—is 
intelligible enough. It is evidently to insure a supply of clean 
fish throughout as large a portion of the year as possible, and 
to enable each river to support the greatest stock—a result 
which could only be obtained by such a provision as the above. 
It is also doubtless intended to insure an equal distribution ‘of 
fish throughout the whole length of the river. These salmon, 
