68 THE ZOOLOGIST. 



is seen, one finds out how numerous they are. This applies 

 chiefly to X. ericetorum (itala) ; X. virgata is easier to see. I have 

 noticed near Oxford that this latter species is very fond of sitting 

 exposed on the most prickly thistles in the neighbourhood. 



With regard to the remaining bright species in the British 

 fauna : C, aspersus more or less harmonises with old walls, &c. 

 Arianta arbustorum and T. nemoralis and hortensis are more 

 difficult to understand. F. E. Beddard* says the colour of 

 Tachea must be either cryptic or epigamic, and very naturally 

 objects to regarding them as sexual in hermaphrodite animals. 

 Eimer and C. Darwin t also agree that sexual selection has not 

 modified Mollusca. 



With regard to the colours of T. nemoralis, Eimer,J quoting 

 Leydig, says the amount of moisture in the air has considerable 

 effect, and adduces in support of his view the various colours 

 found in the Rhine Valley, the colour apparently growing darker 

 as the sea is approached. I have looked about for further 

 evidence, but am unable to find anything; nor do I think the 

 amount of moisture can have very much influence. If it has, I 

 imagine it may be because in humid atmospheres the night and 

 day temperatures are more nearly equal, and that therefore 

 a darker colour can do no harm in the respect of warmth, and 

 may help in concealing the animal. 



It is very hard for us to see here how the ordinary colours of 

 Tachea can be cryptic, and to our eyes they certainly are not. It 

 would appear, too, that they are not so to Thrushes, Blackbirds, 

 &c, which kill considerable numbers. They can hardly be sematic, 

 as the birds are evidently fond of them, for "thrushes' stones," 

 though more obvious in winter, when other food is scarce, may 

 frequently be seen in summer, when worms and suchlike are 

 abundant. 



W. H. Dall§ has suggested that the striped shells of, e.g., 

 T. hortensis lutea, B.F. 12345, are cryptic among the stripes 

 of green and dry grass, &c, on the banks they frequent. I 

 cannot see it myself. 



A good deal has been said about the effects of food on the 

 colour, but experiments seem to give such varying and conflict- 



* ' Animal Coloration,' 1892, p. 56. f ' Descent,' ed. 1871, vol. i. p. 326. 

 | « Organic Evolution,' p. 137, quoted by F. E. Beddard, op. cit., p. 56. 

 § Quoted by J. W. Taylor, op. cit., vol. i. p. 95. 



