where the shells might be expected, giving one the impression that they have 

 temporarily laid aside their houses in order to enjoy more ease or less impeded 

 travel. 



There are in the United States over twelve hundred species and varieties 

 of land snails and slugs and over fourteen hundred fresh-water snails. Some 

 of these may be found in almost every woodland, pond and stream. Slugs 

 often invade our gardens or damp cellars and leave shining trails of mucus 

 vv'hich notify us of their nocturnal wanderings. 



For complete identification of a snail the whole animal or a record of its 

 habitat is usually needed. For example, there is no shell character which will 

 satisfactorily separate the land from the fresh-water snails. If the whole animal 

 is at hand, one can check on other characters. Land snails almost always bear 

 their eyes on the ends of the longer tentacles, often miscalled "'horns". The 

 eyes of most amphibious and water snails are at the bases of the tentacles. Land 

 snails usually have tv^-o pairs of tentacles, while water snails usually have but 

 one pair. Water snails may have either lungs or gills. A snail with gills may 

 have a horny or limy disc, called an operculum, attached to the side of the body 

 in such a position that it serves as a door to the shell when the animal is re 

 tracted. The presence or absence of an operculum and the details of its mark' 

 ings are useful characters for snail identification. 



Another structure examined by experts in snail classification, but not used 

 in general shell identification, is the radula, a tongue-like, rasping organ. One 

 who has kept snails in a well established aquarium has probably noticed the 

 peculiar action of this structure and the ripple-like markings it leaves on the 

 glass, where the snail has scraped off the algal growths. Most snails are largely 

 herbivorous hut a few, such as the land snail, Haplotrema, are carnivorous. 

 Some species may act as scavengers. 



Most of the pulmonate snails are hermaphroditic, while the operculate 

 snails are usually unisexual. Some snails, such as Viviparus, retain their eggs 

 until development is completed, and each little snail has its protective shell 

 formed when it is born. Many snails, however, lay eggs in gelatinous masses. 

 Some, like Helisoma, deposit a flat, rather solid disc of jelly containing about 

 twenty eggs. Others, like Physa and Lymnaea, leave a rather loose and more 

 or less cylindrical mass of jelly enclosing the eggs. A few snails, like Paludes- 

 trina, deposit eggs on the outside of their own shells or on the shells of others 

 of their own species. Several of the land snails and slugs deposit their eggs 

 singly under damp logs and boards, each egg with its coating looking like a 

 pinhead of milky jelly. Some snails lay shelled eggs. Pomacea, the infusoria 

 snail of the aquarist, deposits a mass of shelled, pinkish eggs on some convenient 

 plant or tree trunk above the surface of the water. One large tropical species 

 of land snail lays an oval egg an inch or so long which looks very much like 



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