8 JONES : MOLLUSCAN ALBINISM. 
to the original type. Ina pond everything is in favour of this. 
The animals cannot, in the generality of cases, leave their 
habitat, even if they wish to do so, and provided food be plenti- 
ful there is no reason why they should make the attempt. 
As regards land snails, conditions are very similar. The 
animals do not wander far in search of food as a rule, for every 
collector knows how certain species, or varieties of species, are 
found year after year in the same locality, though that locality 
may be only a few yards across. Single albinos are also 
frequently taken. Last year I took in the Reddish canal a 
single specimen of P. corneus var. albina, and, although I 
searched a whole afternoon most diligently, I was not rewarded 
with a second. But the conditions in a pond and ina canal 
are widely different. In the former the inhabitants are cramped 
into a small space without the opportunity of travelling far, in 
the latter there are currents, together with unlimited space to 
rove over, so that no doubt broods of albinos in the latter get 
widely dispersed, and are prevented from propagating the 
abnornsality. I believe that an albino is such owing to 
constitutional deficiency and not on account of its surroundings. 
Where one finds albinos there are frequently typical individuals 
living on the same food and under similar conditions. 
It is worth while bearing in mind the fact that there are 
some species of mollusca which normally carry an albino shell, 
for instance, Carychium minimum and Hyalinia crystallina, and 
it is possible that such species have been evolved from species 
having coloured shells in a manner similar to that of the white 
varieties mentioned above. Most probably, however, the earliest 
shell-bearing mollusca carried. uncoloured shells, and it is pos- 
sible that such snails as C. minimum and H. crystallina represent 
an older form of shell development, and that albinos are a 
reversion to the original type. 
The popular idea is that a shell in order to be an albino 
must be white. From a scientific point of view this is not 
necessary. Albinism is lack of colour. Then, a transparent, or, 
J.C., vili., Jan. 3895. 
