556 ScHAEFF — On the Slugs of Ireland. 



It seems clear that the sea has some connexion with this variety at any rate, 

 but I think its connexion is only of an indirect nature. It struck me at first that 

 the sides of the slugs might be more stimulated to secrete mucus than the back, as 

 the animals would have to crawl over gi'ass which must be coated with depositions 

 of salt ; but why should they not then all be of that variety near the sea? Entirely 

 black ones are, in fact, rather more common. 



There is another more likely explanation to account foi- the fact of the 

 bicoloured dress of the young being retained in the adult on the sea-shore. 

 It appeared to me that in the twilight of morning and evening the black-and- 

 yellow forms might have equal advantages of concealment with the black ones, 

 when crawling among the stones at the .sea-shore, for I believe this species is just 

 as much preyed upon as other slugs by the innumerable birds frequenting Dublin 

 Bay. It is well known that the gizzard of gulls is frequently found to be filled 

 with slugs of all kinds, whilst Thompson (43) often found the shell of Limax 

 maximus and Agriolimax in the stomach of the thrush. 



The only place where I have found the claret-coloured variety was in pine 

 woods at Killakee and Howth, where the general colouring of the ground 

 resembles that of the slug, and at once suggested to me the protective character 

 of its colour. As regards the young winter forms of Avion ater, I have always 

 noticed that they choose the yellow fallen leaves, whose colour they resemble very 

 closely, for hiding-places, and here again it is the need of protection and not 

 temperature which influences their colouring. 



As for the other species of slugs, we have very good examples of protective 

 colouring in Limax marginatus, Amalia carinata, Avion vitevmedius, and Geomalacus 

 maciilosus. The first, when on a tree-trunk, which is its favourite haunt, is easily 

 mistaken for a piece of bark ; the second resembles the ground in which it spends 

 almost its entire existence ; the third looks very like a little fungus just coming 

 out of the ground, while the last imitates the colour of the lichen among which it 

 lives to a remarkable degree. 



In the other slugs protective colouring is perhaps not quite so ajDparent, but I 

 have no doubt that in all cases their colour is mainly influenced by the natural 

 selection of those best suited to escape the keen sight of their enemies. 



