SNAILS OF POND, RIVER, AND BROOK 



On the Saturday following the trip to the river and creek, the large 

 museum in the park was visited, and under the guidance of Professor 

 Parker we studied the shell collection, and particularly the specimens 

 from fresh-water streams and ponds. The Professor was thoroughly 

 acquainted with this class of animals, and narrated many interesting 

 facts as we went from case to case. 



" Our fresh-water snails," he said, " may be divided into two classes: 

 first, those which breathe by means of a lung and which must come 

 to the surface at regular intervals to take in a supply of air; and 

 second, 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 

 Limnceidce, comprising the pond snails. These animals generally have 

 a long, graceful shell, horn-colored for the most part, but sometimes 

 greenish without and reddish within the aperture. They have a broad, 

 flat foot; an auriculate, or eared, head ; and flat, triangular tentacles. 



" It is interesting to note that the young animals breathe air through 

 the water for a long time, but finally acquire the normal character- 

 istic of the family, which is, breathing the air directly. While sub- 

 merged, the mantle chamber containing the lung is tightly closed, 

 so that no water can possibly enter. It is thought by some that the 

 species of I/imncea, living at great depths in large lakes, retain the 

 early habit of allowing the water to fill the mantle cavity and so breathe 

 oxygen through the water. They are not therefore compelled to come 

 to the surface for air. 



" I/imnceas live under many varying conditions, being found in the 

 arctic regions of Greenland and Iceland as well as in the tropics, 

 in thermal springs, and those containing sulphur and other mineral 

 matter as well as in brackish and in fresh water. In Thibet, they 

 have been found at a height of over fourteen thousand feet, and in 

 Lake Geneva, Switzerland, at a depth of eight hundred feet. 



" During times of drought, when streams are dried up and the sur- 

 face of the mud is sun-cracked, the species of the family bury them- 

 selves deeply in the mud and cover the aperture with an epiphragm 



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