MASEFIELD : THE ECONOMIC USE OF SOME BRITISH MOLTATSCA. 1 57 



where we live 200 people to the acre, and expect to find shells as little 

 as ferns." 



Our arboreal species of molluscs spend the summer and autumn 

 months on the trunks and amongst the branches of many of our forest 

 trees, keeping them clear of deleterious and decaying matter, and I 

 believe many species ascend our forest trees to feed upon the honey- 

 dew on the leaves. 



The Testacellidas, again, feed exclusively on worms, and assist in 

 keeping their numbers down, and so help in preserving a healthy 

 balance of nature; whilst the subterranean dweller, Ccecilioides acicula, 

 acts the part of scavenger underground. Mr. Shrubsole states that a 

 gardener near Chester purposely keeps Testacellce to kill the worms 

 in his fernery. 



Further, if we examine our inland waters, we find them all teeming 

 with molluscan life, without the presence of which all these waters 

 would soon become seriously contaminated with decaying animal 

 matter, and choked up with confervoid growths. This is well known to 

 all who keep aquaria, wherein it is absolutely necessary to preserve a 

 proper balance of animal and vegetable life to maintain the water in 

 a pure state and the glass clear. The presence of our large bivalves 

 ( Unio, Anodon, Sfl/zcerium, Dreissensia, and other syphon possessors) 

 contributes to maintain clearness and purity of water in muddy lakes, 

 canals, and ponds, as their chief food consists of infusoria and other 

 floating organisms. But perhaps some one may say that these mol- 

 luscs can only perform these useful duties in summer and autumn, if 

 they hibernate during the winter and early spring ; but this is not so. 

 Several species, such as Helix fusca, H. cafterata, Vitrina, and others, 

 become active during the winter months, except in severe frosts, and 

 I have seen Vitrina many times crawling over snow in search of food. 



As to the variety of food of our mollusca, it is almost endless, but 

 amongst other things which they devour greedily is waste paper of all 

 kinds when reduced to a pulpy state by water or rain, and even 

 bivalves revel in this food. They also live on dead insects of all 

 kinds, including flies, moths, and butterflies, and on one occasion 

 Helix aspersa was found feeding on the decaying eggs in a deserted 

 bird's nest, having first perforated the shell to get at such a choice 

 morsel. I hope I have now stated sufficient facts to show that our 

 mollusca are amongst the most useful of nature's scavengers, and also 

 how very plentifully they are distributed over the length and breadth 

 of our land ; but if anyone is still sceptical, I can only repeat, let him 

 sally forth any damp night, and he will soon discover for himself that 

 no decaying or unhealthy matter escapes the attention of our slugs 

 and snails, which, I maintain, are some of our best friends in the 

 preservation of the health of man. 



