The number of cercariae produced by the pullulating rediae in a single water-snail is immense, and as they are emitted at a given period or a few successive periods, the snail at these times appears enclosed in a cloud of whitish flocculent matter.
There is not a very large amount of food-material present in the egg of this snail, and accordingly the cells resulting from division are not so unequal as in many other cases.
So too the acrembolic eye-tentacle of the snail has a complete range of movement, and also the pleurembolic proboscis of the Rhabdocoel prostoma.
Moreover, long habituated to snail-like modes of travel, the people did not rapidly appreciate the celerity of the locomotive.
The mound builders, Pueblo tribes, middle Americans and Peruvians, were potters of many schools; gorgeous colour fascinated the Amazonians, the Patagonians delighted in skins, and even the Fuegians saw beauty in the pretty snail shells of their desolate island shores.
Amongst the orbweavers of the family Argyopidae there are species belonging to the genera Cyclosa and Cyrtophora which closely resemble small snail-like gastropods as they cling to the underside of leaves with their legs drawn up. Other members of the same family - like Araneus coccinella, and Paraplectana thorntoni- imitate beetles of the family Coccinellidae which are known to be distasteful; and certain genera of the family Salticidae (Homalattus and Rhanis) closely resemble small hard-shelled beetles.
The liver-fluke (Distomum hepaticum) passes through its larval stages in the water snail Limnaea truncatula in Europe; in L.
The attention of birds is speedily attracted to the snail by this appearance and by the peculiar movements which the worm executes, and the passage of the parasite into its final host is advantageously effected.
Distomum macrostomum, which occurs in various birds, produces a very curious sporocyst in the body of the snail Succinea putris.
In England the word "snail" in popular language is associated with Gasteropods which inhabit land or fresh water, and which possess large conspicuous spiral shells; terrestrial Gasteropods, in which the shell is rudimentary and concealed, are distinguished as "slugs."
In many cases it appears that only the brilliantly coloured tentacle is pecked off by the bird, and as the snail can easily regenerate a new one, this in turn becomes infected by a fresh branch of the sporocyst ramifying through the snail and thus a new supply of larvae is speedily provided (Heckert).