46 DR. J. MURIE ON IRREGULARITY [Jan. 13, 
4, The depth of the body and root of tail differ as regards aug- 
mentation, the former being as 8 to 1, the latter as 5°9 to 1. 
5. Between the width and depth of the operculum, respectively 
5:7 and 7 to 1, the horizontal to vertical increase is inversely to 
what obtains in the body. 
Availing one’s self of these considerations, and comparing speci- 
mens I. and II. with III. (Table B), it will be seen, more especially in 
the older fish, II., that the maxillary bone and distance from snout 
to eye are proportionally larger than in the Parr. The same may 
be said as regards growth of the operculum, more particularly its 
depth. The distance between the ventral and anal fins is also 
sensibly greater. Thus those parts which in the adult, ceteris pari- 
bus, show the greatest relative accretion are, curiously enough, in the 
Salmonoids reared in fresh water, the parts which have most incre- 
ment. From this it follows that whilst a general arrest of develop- 
ment, retardation of growth, or whatsoever the term used, has oc- 
curred from the altered physical circumstances, still the proportional 
magnitude of the parts has kept pace with that of a normally deve- 
loped adult Salmon favoured by visits to the sea. 
GENERAL CONCLUSIONS. 
The main fact at issue—Can Salmo salar live for series of years 
in fresh water without access to the sea ?—if not settled beyond cavil, 
has, I venture to think, in this and the preceding paper, been tole- 
rably well substantiated. At least the evidence of many observers 
has been given; so that it remains for those who discountenance 
the view to show the fallacy of the data, and prove on evidence as 
reliable that the contrary is the true state of the case. This does not 
interfere with the necessity of further experiments being tried. For 
my own part, I am quite willing to bow acknowledgment to which- 
ever side the truth lies on—though, after an impartial consideration, 
I cannot escape or reason away the strong presumptive allegations 
positively confirming the opinion. To me they are reasonable, be- 
cause based on what, in homely parlance, are deemed everyday occur- 
rences. The principle in the life-history of the Salmon which seems 
at variance with its customary habits is in reality not so; what takes 
place as a general rule is here but temporarily departed from. In 
the physical constitution of animals, the limits assigned to the well- 
being of the individual are not so rigidly exact as a mathematical 
problem ; hence, to judge rightly, we must know all, or be prepared 
to confute abnormal phases of existence. In the present instance 
the choice of credence lies between testimony harmonious with laws 
regulating the primary growth of Salmon, and suppositions framed 
on circumstances we have but an imperfect knowledge of, unless it 
be satisfactorily shown that the statements of such a truthful ob- 
server as Yarrell, or the instance recorded by Anderson, are fictitious 
or egregiously false. 
Those who deny that some Salmon, few or many, can permanently 
accommodate themselves to a freshwater residence for a comparatively 
