114 



INTRODUCTION TO ZOOLOGY 



Hiberna- 

 tion. 



Enemies. 



Limnaea seems to spend the greater part of 

 the winter in a state of torpor, buried in the mud 

 at the bottom of the pond and breathing probably 

 through its skin ; it does not hibernate completely, however, 

 and has been seen even on a day when the pond was frozen 

 over, crawling about on the under side of the transparent ice. 

 The water snail is preyed upon by a good 

 many other creatures; ducks and water-shrews 

 devour it, the carnivorous water beetle (Dyticm marginalis) 

 the " shark " of the pond feeds on it, frogs and toads will 

 snap it up when small, and sticklebacks and other fish eat 



a great quantity of the eggs 

 before they hatch and of the 

 recently hatched fry. 



Other Common Air-breathing 

 Water Snails. 



There are four chief genera 

 of lung-breathing water snails, 

 and there are several species of 

 each genus that are very common 

 in our ponds ; these will be now 

 briefly enumerated and shortly 

 characterised, so that they may 

 be recognised when found. 



Belonging to the 

 Limnaea g enus Limnaea are all 

 waters nails with thin, 

 horn - coloured, spirally - coiled, 

 conical shells, and having two 

 triangular, non-retractile ten- 

 tacles, with an eye at the base 

 of each. 



Limnaea stagnalis (the Common 

 Pond Snail) (Figs. 61 and 65). 

 This is the species fully de- 

 scribed above. Size 1J to 2 

 inches. Whorls 6 to 8, the last 

 one relatively very large. Mouth of shell rather more than 

 half the whole length of the shell. 



L.aur 



rune. 



FIG. 65. The Shells of some 

 common species of Limnaea. 



L. stag., Limnaea stagnalis ; L. pal., L. 

 palustris ; L. per., L. peregra ; L. 

 aur., L. auricnlaria ; L. trutic., L. 

 truncatula. 



