But there are a considerable number of snails, both terrestrial and aquatic, which are not Pulmonates.
Snails are reared in some parts of the country as an article of food, those of Burgundy being specially esteemed.
They live for some time in water or mud, occasionally entering the bodies of water snails, but undergo no change until they reach the lung of a frog, when the cycle begins anew.
Although several species belonging to the second class occasionally enter the bodies of water snails and other animals before reaching their definitive host, they undergo no alteration of form in this intermediate host; the case is different, however, in Filaria medinensis and other forms, in which a free larval is followed by a parasitic existence in two distinct hosts, all the changes being accompanied by a metamorphosis.
The so-called eelworms (Nematodes) may do immense damage on roots and in the grains of cereals, and every one knows how predatory slugs and snails are.