98 



all the pale and albino forms came from Valentia Island and 

 from Beginnis Island, close to Valentia. Also, in a collec- 

 tion from the great Skellig Island, twelve miles off the 

 Kerry coast, there were numerous examples of Hyalina 

 alliaria, nearly all of which were without pigment. Here, it 

 may be, the exposed situation had something to do with the 

 formation of these varieties ; but never having visited the 

 localities it is not easy to suggest what physical causes may 

 have been at work in the matter. 



I have not been able in any case to discover that albinism 

 of the shell is of service to the individuals in which it occurs ; 

 on the contrary, in the case of Helix aspersa, I believe that 

 the white examples are more easily seen, and so more often 

 destroyed by birds. 



Hence it would seem that albinism is, on the whole, 

 retrogressive, scarcely, perhaps, equivalent to mere disease, 

 because congenital, and transmitted, and not harmful to the 

 constitution of the organism — due to some hitherto un- 

 explained conditions, and arising under these conditions in 

 any, or almost any, pigmented species. 



Yet there is one genus at least in which — whatever its 

 value to the species — albinism seems to have become a pro- 

 gressive and developing character. This is the genus 

 Hyalina, to which I have already referred. In Hyalina 

 cellaria and H. nitidula, white varieties are rare enough to be 

 classed as aberrations or occasional sports ; but H. excavata 

 has the colourless form much more frequent, while H.pura 

 is as common colourless as coloured, and lastly, H. crystallina 

 is always and constantly albino. Here, certainly, it looks as 

 though we had before us various stages in the development 

 of white species from coloured ones, through the trans- 

 mission of a peculiarity which first arose as a mere chance 

 aberration. 



These, that I have spoken of, are albinisms of the shell, in 

 which pigment glands on the mantle have not developed, 

 and so the shell has not been coloured ; but albinisms do 

 occur in the slugs, in which the pigment is quite wanting 

 from the skin, such, for instance, was a pure white example 



