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, hin- 
dering normal growth. Had the Salmonoids gone to the sea and re- 
turned 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 ma- 
terial 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, H. Widegrent has already 
attempted to show, and has partly been supported and opposed by 
Malmgrent 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 Salmonidze 
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 faint distinctions of the Salmonidz 
to a chaos. 
On the other hand, can it be that in this variability from a com- 
mon 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 oppo- 
site 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. 
+ Gfvers. Vetensk. Akad. Forhandl. 1863. 
{ Kritisk Gifversigt af Finlands Fisk-Fauna: Helsingsfors, 1863. Translated, 
Wiegm. Archiv, 1864, and reviewed, Record of Zool. Lit. 1864, p. 178, by 
Giinther. 
Proc. Zooxt Soc.—1870, No. IV. 
