SNAILS OF POND, RIVER AND BROOK. 



Many of my readers have doubtless 

 kept an aquarium at some time in their 

 life and have stocked it with several gold- 

 fish, a small turtle and some fresh water 

 snails. They have also, without doubt, 

 stood in front of the aquarium and 

 watched the strange antics of each of the 

 three kinds of animals and have won- 

 dered at the swiftness with which the little 

 snails progressed about the glass sides of 

 the artificial pond. It is of these mol- 

 luscan denizens of fresh water that I shall 

 write in this article. 



In the fresh-water species the shell is 

 not often rounded like that of the land 

 snails, but is more frequently long and 

 pointed, the spire resembling a church 

 steeple. The animal, too, differs very 

 greatly, the tentacles being either flat and 

 triangular or long and very tapering. The 

 eyes are not placed at the end of the eye- 

 peduncles, as in the land shells, but are 

 generally situated on little swellings at 

 the base of the tentacles. They may be 

 found in almost any body of water, ad- 

 hering to stones, sticks, and other sub- 

 merged objects, or crawling over the 

 sandy or muddy bottom. 



Our fresh-water snails may be divided 

 into two classes; first, those which 

 breathe by means of a lung and which 

 must come to the surface at regular in- 

 tervals to take in a supply of air, and, sec- 

 ond, those which breathe by means of 

 plume-like gills which take the oxygen 

 directly from the water. . 



One of the most common and best 

 known of the first class is the Limnaeidae, 

 comprising the pond snails. These ani- 

 mals have generally a long, graceful shell, 

 horn-colored for the most part, but some- 

 times greenish without and reddish with- 

 in the aperture. The animal has a broad, 

 flat foot, an auriculate or eared head, and 

 flat, triangular tentacles. The habits of 

 these animals are very interesting. They 

 will wander about the sides of an aquar- 

 ium, eating the growths of green scum 

 which have collected. At this time the 

 mouth may be seen to open, exposing the 



radula and the operation of eating is not 

 unlike the motions of a cat lapping milk. 

 They are such voracious eaters that the 

 dirtiest aquarium will be cleansed by 

 them in a very short time. It is interest- 

 ing to note that the young animals 

 breathe air through the water for a long 

 time, and finally acquire the normal char- 

 acteristic of the family of breathing the 

 air directly. While submerged, the man- 

 tle chamber containing the "lung" is 

 tightly closed so that no water can pos- 

 sibly get in. It is thought by some that 

 the species of Limnaea living at great 

 depths retain the early habit of allowing 

 the water to fill the mantle cavity and so 

 breathe oxygen through the water and 

 are not, therefore, compelled to come to 

 the surface for air. 



Limnaea lives under many varying 

 conditions, being found in the arctic re- 

 gions of Greenland and Iceland as well as 

 in the tropics, in thermal springs and 

 those containing mineral matter, as sul- 

 phur, as well as in brackish and fresh 

 water. They have been found at a height 

 of over fourteen thousand feet in Thibet 

 and at a depth of eight hundred feet in 

 Lake Geneva, Switzerland. During 

 times of drought when the streams are 

 dried up and the surface of the mud is 

 sun-cracked, the species of this family 

 bury themselves deeply in the mud and 

 cover the aperture with an epiphragm, in 

 much the same manner as the land shells. 

 This fact accounts for the apparent disap- 

 pearance of all life from a pond when it 

 dries up, and its sudden and seemingly 

 unaccountable reappearance when the 

 pond is again filled with water. 



A genus of pond snails closely allied 

 to Limnaea, but having discoidal or 

 spiral shells, is Planorbis, the flat-orb 

 shells. Instead of dragging their shells 

 after them, as in the last genus, they carry 

 them perfectly perpendicular, or perhaps 

 tilted a little to one side. The animals 

 are very rapid in movement, more so than 

 Limnaea, which are rather sluggish. 

 They delight in gliding rapidly about, 



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