Various species among those that are predaceous attack smaller insects, hunt in packs crustaceans larger than themselves, insert their narrow heads into snail-shells to pick out and devour the occupants, or pursue slugs and earthworms underground.
So too the acrembolic eye-tentacle of the snail has a complete range of movement, and also the pleurembolic proboscis of the Rhabdocoel prostoma.
- Developmentof the River-Snail, Paludina, vivipara.
- A Series of Stylommatophorous Pulmonata, showing transitional forms between snail and slug.
The generative apparatus of the snail (Helix) may serve as an example of the hermaphrodite apparatus common to the Pulmonata and Opisthobranchia (fig.
In this duct and sac the spermatophores received in copulation from another snail are lodged.
The pond-snail (Limnaeus) furnishes, on the other hand, a very beautiful case of distinct ganglia and connecting cords (fig.
- Nervous System of the Pond knob - like particle Snail, Limnaeus stagnalis, as a type of the (Neritina and Palu- short-looped euthyneurous condition.
- Hermaphrodite Reproductive Apparatus of the Garden Snail (Helix horlensis).
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.
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."
Hortensis is a variety, is one of the commonest forms. Helix pomatia, L., is the largest species, and is known as the "edible snail"; it is commonly eaten in France and Italy, together with other species.
Ichthulin (see above) may be placed in this group; " helico-proteid," found in the serous gland of Helix pomatia, the vineyard snail, also belongs here.
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.
The liver-fluke (Distomum hepaticum) passes through its larval stages in the water snail Limnaea truncatula in Europe; in L.
Distomum macrostomum, which occurs in various birds, produces a very curious sporocyst in the body of the snail Succinea putris.
This sporocyst assumes a branched structure and penetrates into the tentacles of the snail (fig.
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.
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).
- There are 57 species of Helix (maimailsuburi, dedemushi, katatsumuri orkwagyu) and 25 of Clausilia (kiseru-gai or pipe-snail), - including the two largest snails in Japan, namely the Cl.
Moreover, long habituated to snail-like modes of travel, the people did not rapidly appreciate the celerity of the locomotive.
The cavity of the tube of Helicopsyche, composed of grains of sand, is itself spirally coiled, so that the case exactly resembles a small snail-shell in shape.
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.
In the Limnephilidae the maxillary palp is three-segmented in the male, the larvae are variable in habit, many forming cases of snail-shells.
- Development of the Pond-Snail, Limnaeus stagnalis.
- Development of the River-Snail, Paludina vivipara.
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 Romans are credited with having purposely introduced the edible snail (Helix pomatia) into England, and the common garden snail and slugs (Helix aspersa, Limax agrestis and Anion hortensis) have been unwittingly established in New Zealand.