In small flowers which are crowded at the same level or in flat flowers in which the stigmas and anthers project but little, slugs or snails creeping over their surface may transfer to the stigma the pollen which clings to the slimy foot.
The same general range of body-form is shown in Pulmonata as in the Heteropoda and in the Opisthobranchia; at one extreme we have snails with coiled visceral hump, at the other cylindrical or flattened slugs (see fig.
It is about a foot in length, lives on snails and worms and is provided with both lungs and gills.
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.
Thus the whole of the Pulmonata (which breathe air, are destitute of gill-plumes and operculum and have a complicated hermaphrodite reproductive system) are either snails or slugs.
The fresh-water snails which are not Pulmonates are the Paludinidae, Valvatidae and Ampullaridae, together with Neritina, a genus of the Neritidae.
Now, Coccinellidae (ladybirds) are known to be highly distasteful to most insectivorous mammals and birds, and snails would be quite unfit food for the Pompilid or Ichneumonid larvae, so that the reason for the mimicry in these cases is also perfectly clear.
The species of Helix are all herbivorous, like the Pulmonata generally; snails and slugs are well-known enemies to the gardener.