imflue:nce of food and temperature on pigmentation. 329 
been satisfactorily worked out, it has probably diverged and varied in 
response to environment from a comparatively simple and more or 
less uniform tint of animal and shell towards the more striking and 
distinct colours they now so fre({uently exhibit, the more fugitive and 
advanced colours being the result of greater chemical activity and 
change amongst the constituents of the body, and are probably those 
most recently ac(piired and which have not yet become an integral 
and permanent part of the organization. 
Food has been undeniably demonstrated to modify the colours of 
certain insects and birds, and it is probable that a particular diet will 
to some extent modify and iiiHuence the intensity and character of 
the pigmentation in the mollusca. Mr. Hawkins, in “The Ncituralist” 
for February, 1899, has i)ublished some practical observations on the 
apparent inlluence of food upon the colours of the shells of Helices, 
which it would be of the greatest interest to confirm or refute. 
Cold has been demonstrated to inhibit the formation of the red 
pigment, but to be favourable to the development of the black, which 
is generally due to Melanin, a substance which is practically identical 
with the colouring matter of the cephalopod ink and is usually found 
in minute particles in the dermal epithelial cells as well as in those 
of the other parts of the body, its greater abundance being correlated 
with superior physical vigour, as it is in relation to and in a great 
measure dependent upon the mass of blood in the organs from which 
it is secreted and deposited in the external integument in response to 
external influence, the effect of cold being demonstrated by Simroth 
to induce darkne.ss of colouration in the slugs, especially if they are 
subjected to its influence during spring, at the period of their most 
active gTOwth and development. 
A further confirmation of this law of colouring is afforded by the 
observation of the Rev. Dr. Xornian of the darkening A griollmax 
agrestis under the diminishing temperature of autumn and by the 
known fact that Limax cinereo-nigtr, the northern race of Liniax maxi- 
intis, is often totally black, while in warm Italian regions the species 
develops a series of brilliantly colmired and strikingly marked forms. 
Limax marginatm^ (Mull.) offers still more striking confirmatory 
evidence of the effect of cold and moisture in inducing melanism. 
In the north and north-western parts of this country and on 
mountain sides this species becomes darker in colour and loses the 
glaucous and translucent aspect which is its usual characteristic on 
