VARIATION IN COLOUR. 
‘J2 
etc., Ibvnied tlie new growtli of a much darker colour than before, 
although it is possible that in this case the different result may be 
due to the additional articles of diet not enumerated. 
According to iM. INlalard and other observers concealment by 
isochromatic adaption to environment is very common amongst 
crustaceans and other organisms, and we apparently see a striking 
e.xample of this interesting phenomenon in the albine .specimens of 
Papa cijlind raced found by Capt. Farrer upon a whitewashed wall at 
Bassenthwaite, the white variety being contined exclusively to the 
whitewashed portion, the type form existing only upon that part of 
the wall left in its natural condition ; as collateral evidence of the 
probable accuracy of the supposition that we have here a case of this 
i.sochromatic adaptation to environment, without, however, defining 
the [)rocess by which this adaptation has been brought about, wdiether 
by the elimination of the normal form or other method, I may recall 
the record given by Semper, on the authority of Dr. Braun, that white 
rabbits are most certainly and easily reared in a white reflected light. 
It is now well-known and acknowdedged that albinism is hereditary 
and may be transmitted to offspring. This is not only practically 
established by experience of the shells under natural conditions, but 
has been fre(piently demonstrated with mollusks kept in captivity. 
The increase in numbers of the .specimens of a white variety, to 
the di.sadvantage of the ty[)ical form dwelling w'ith it, points only to 
the persistence of some features of the environment favourable to 
the variation or, according to (Jredler, indicates that the species has 
reached the extreme limit of its horizontal or vertical distribution. 
There appears to be a somewhat general consensus of opinion, 
especially amongst Continental conchologists, that albinism in the 
shell occurs most freely amongst tho.se mollusks inhabiting cold, 
misty and sunle.ss localities, and the unusual numbers chronicled by 
them during dull and sunless seasons and from subalpine districts, 
which have something of this character, supports the theory, as also 
does the assertion of Herr Dietz that e.xamples of IJelu' hertemh of an 
albino character are most commonly found in wet years, and that those 
with banded shells in normal seasons, have the growth of a wet season 
deficient of the usual pigment. 
Diametrically opposed to the preceding theory is the suggestion 
that dry, warm and sunny seasons are favourable to shells assuming 
the albine state, and there is some reason from analogy in believing 
