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Show 1870.] IN THE GROWTH OF SALMON. 49 to say, after the fry have reached a certain grade of maturity and bulk, causes (nature of food and retention in a limited volume of fresh water) induce malnutrition or derangement of nutrition, hindering normal growth. Had the Salmonoids gone to the sea and returned stunted, the term "arrest" would still be partially applicable, inasmuch as normal evolution from the embryonic to the full-formed animal would have been interfered with, or remained stationary short of completion. The phrase would be equally a happy one, viewing the development of Salmon as a series of stages of progressive growth, as Mr. Buckland puts it; for as some physiologists limit "growth" solely to increase of size, and "development" to structural change*, the idea of progressive advance in the Salmon would sanction the " arrest of development" as a most suitable term. Should future researches support the facts and views it has herein been endeavoured to establish, obviously many species at present adopted in the nomenclature of the genus Salmo may require material modification. For doubtless it would follow that the same fish, under different grades and shades of development, has been distinctly and separately named, as, indeed, II. Widegrenf has already attempted to show, and has partly been supported and opposed by Malmgren*]; and Giinther. The geographical distribution of the group as now understood might need revision. It would likewise strike at the root of living transitionary species, and be the clue whereby a path through the labyrinthine variations of the Salmonidse would lead to a better knowledge and study of the group. Assumed hybridity of Salmonoids must necessarily require a much broader body of evidence, and more vigorous scrutiny of data, than has hitherto been accorded it. Although it may be said that fish-spawn presents far greater accessibility to the fecundating influence of the milt of a different species than does the union of the germinal products of higher Vertebrata, still the line of demarcation must rest sharply somewhere; otherwise no such thing as specific identity would be recognizable in the produce; instead of hybrids being rare, or in the minority, as now obtains, they would soon be in overwhelming majority, and reduce the present taint distinctions of the Salmonidse to a chaos. On the other hand, can it be that in this variability from a common stock we have tracings of the elimination of natural species ? Has the inherent organization, permitting some individuals to survive changed conditions, alone the utility of preserving the race, or does it carry with it the elements of structural variety, whereby ultimate scission from the primary type is effected? There are not wanting able defenders of views of an entirely opposite character ; but in whatever direction the opinion leads, the force * See some pertinent remarks thereon in Darwin's 'Animals and Plants under Domestication,' vol. ii. p. 389. f GSfvers. Vetensk. Akad. Forhandl. 1863. + Kritisk OCfversigt af Finlanda Fisk-Fauna: Helsingsfors, 1863. Translated, Wiegm. Archiv, 1864, and reviewed, Record of Zool. Lit. 1864, p. 178, by Gunther. PROC. ZOOL Soc-18/0, No. IV. |