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Show 34 DR. J. M U R I E O N I R R E G U L A R I T Y [Jan. 13, was run off, when three good-sized Salmon were found to have survived ; these were bright, lively, and healthy, but ill-grown. One of these specimens sent to London weighed 15 oz., measured 14TJ inches in its greatest length, and had a girth of 6^ inches. The head was 3± inches from the snout to the extremity of the operculum, and appeared large enough for a 5-lb. fish. It is greatly to be regretted one of these three unusually interesting specimens was not preserved in spirits and forwarded to the British Museum. 6. Lastly, I shall advert to an account, by Mr. Frank Buckland, of a " Salmon that had never seen the sea "*. This specimen was obtained from the river W y e in 1862, in the Parr condition, and transferred to a pond through which a streamlet of water ran. Four years afterwards it was taken out as a Salmon 11 inches long. IV. Irregularity of growth.-The life-history of Salmo salar, as all admit, is a most extraordinary one. The exceeding rapidity of their growth between their descent to and return from the sea is marvellous. But there are still two points as remarkable, viz. that a retardation of development is far from uncommon ; and, on the other hand, causes occasionally ensue seeming as it were to stimulate and quicken the usual accession of growth. Since Shaw's experiments on the growth of Salmon-fry f, other observers have noted, and, in fact, it is now universally known to all those practically conversant with artificial Salmon-culture, that of the first year's Smolts only some migrate seawards, while many of them remain behind in the fresh water. In the second year it also occasionally happens that in some fish no desire of migration ensues; but the accession of migratory instinct takes place in the ensuing season, or even later. Iu other words, some Smolts ripen earlier than others, and those remaining behind, which are slower in their seasonal migratory instinct, remain apparently stationary as to growth. The cause of the retardation of the migratory stimulus, so far as I am aware, has not been satisfactorily accounted for; but clear evidence exists that the young self-detained Salmon are little or no larger than their brethren a year or two younger. Their development is more or less retarded for the time being-but not necessarily continuously so; for as soon as migration occurs, the usual growth concomitant with a sea-water visit takes place. Here, then, we have, from natural causes, retention and arrest of growth of young Salmon in a comparatively healthy condition in fresh water for two years or more. If such a fact or premise be granted, it seems to follow, as a necessary consequence, that if Salmon arrived at the Parr condition be prevented from migrating, they either remain stunted or increase in magnitude in a very diminutive ratio compared with their fellows that have spent a season in the sea-water. Regarding increase of size generally, and also unusual accretion of growth, in Salmonoids, this, as most authorities agree, is greatly, if not entirely, dependent on the abundance or scarcity of food, * Figured and described in ' Land and Water,' vol. i. June 2, 1866. t Trans. Roy. Soc. Edinb. vol. .xiv. &e. |