170 FBESH-WATEE AQUAKIA. 



" Fresh-water Winkle," is a favourite witli aquarium-keepers, 

 and as it seems to prefer to feed upon decaying vegetation, it is 

 very useful in the tank. It is much more prolific and more 

 active than its near relative P. contecta, and it also, as its 

 specific name implies, brings forth its young alive. More 

 than eighty fry in different stages of growth are said to 

 have been counted in the ovary of a female of this species. 

 The "Fresh-water "Winkle," unlike P. contecta, clings most 

 tenaciously to that substance to which it may be adhering 

 when touched. Sometimes, indeed, it seems as though the 

 animal would be injured in the attempt to detach it from the 



Fig. 115. Paludina vivipara. 



side of an aquarium. Under such circumstances it should 

 be gently slid up the glass or side imtil it is above the^ 

 surface of the water, when, as a rule, it will immediately 

 let go its hold. The right tentacle, when it is shorter and 

 thicker than the left, distinguishes the male. 



Bythinia tentaculata (Fig. 116) is an interesting little 

 snail, found more or less abundantly in the slow-running 

 rivers, ponds, canals, and ditches of nearly every part of 

 Britain except Scotland, where it is rather local. It is ovi- 

 parous, and deposits its eggs, arranged in two or three rows, 

 in an oblong mass upon stones, the stalks and leaves of 

 aquatic plants, and, in addition to these, while in confine- 



