3634 Habits of the Water-snail and Stickleback 



stagnalis for this purpose, but was soon obliged to substitute some 

 less voracious inhabitant for my small domain, for I found that as it 

 grew in size its appetite increased to an enormous extent, and the 

 plants were punished most severely, the leaves of the Vallisneria spi- 

 ralis being bitten quite through ; and if the snails were in too large a 

 number, the whole of the vegetation was rapidly removed: other vari- 

 eties of the Limnea were consequently introduced at an early period, 

 namely, L. auric ularia and L. glutinosa, as also Physa fontinalis, Bi- 

 thinia tentaculata, Planorbis corneus, and P. carinata. These last 

 two varieties have been found highly serviceable, as from the cornuted 

 formation of their shell and small mouth, the fish cannot so readily 

 get them out to feed upon. With the L. auricularia and L. glutinosa 

 this is easily effected in consequence of the large aperture of their 

 shell ; and if the fish fails in his endeavours by a sudden attack to 

 shake the snail out, he will attempt to suck it from its retreat, as is the 

 case with the gold-fish ; with the minnow (Leuciscus Phoxinus), how- 

 ever, it is different, as the smallness of its size renders this manoeuvre 

 impossible, unless the snail be very minute ; it has recourse therefore 

 to another and quite as efficient a means of obtaining its object, and I 

 have seen these beautiful little fellows seize on their prey and shake 

 it, as a terrier dog would a rat, between a piece of the rock-work and 

 the glass, until they have broken its thin and delicate shell to pieces, 

 and having effected this to their satisfaction, quietly consume their 

 victim. 



It will be seen from these facts, that the snails will require to be re- 

 newed at intervals, particularly as I have previously shown that the 

 increase of the snail by its eggs, which are deposited in very large 

 quantities, is entirely prevented from the fish consuming them the in- 

 stant they exhibit signs of locomotion. 



These water-snails have the extraordinary power of moving along 

 the surface of the water with great rapidity with their shells downward, 

 the foot being attached as it were to the atmospheric air. The Pla- 

 norbis also can fix itself, without any apparent means of attachment, 

 by its side to the flat surface of the glass, and will remain thus for 

 several days. 



In watching the movements of the Limneae, I was for some time 

 under the impression that they had a power of swimming or sustaining 

 themselves in the water, as they would rise from the bottom of the 

 pond, a portion of the rock-work, or a leaf of the plants, and float for 

 a considerable period, nearly out of their shells, without any apparent 

 attachment, and by the contortions and gyrations of their body and 



