122 
ANIMAL LIFE ON THE 
Descending to the bank we step out into the river 
upon a little shelf of rocks, whose rounded ridges, just now, 
here and there, rise above the surface of the flowing stream, 
and hold within their keep a few quiet pools of clear water. 
The quick running ripple of the river has no living thing 
to reveal to us that we can see, and we turn to the pools. 
Lined as they are with a coating of dark-green herbage 
and moss, to the casual visitor there is nothing else to 
discover in them, but the practised eye of the zoological 
student, with a little attention, soon descries the familiar 
form of the litorina, or common yellow whelk of the shore, 
in his little fresh-water brother the paludina vivipara. The 
shell is a little larger than the garden green pea, but is 
found in other waters very much larger, and possibly may 
be so in other parts of the Clyde. The shell is very brittle 
and extremely thin, and is of a dark skin-colour, tinted 
with a light tinge of sap green, consequently, on the spots 
it frequents, it is not very easily seen ; but it seems to be 
plentiful here, for a handful can be gathered in a few 
minutes. Let us now take the creature up, and placing 
him in our glass of water, apply the lens. First we note 
the absence of the operculum^ or lid, as in others of the 
same family, and also those of our salt-water tribes ; and if 
there be anything of the kind, it must partake very much 
of the colour and consistency of the creature's body. We 
have not long to wait for him coming out of his shell, and 
applying the lens, we see, as shown in the accompanying 
illustration, that the foot is somewhat heart-shaped, and of a 
sickly white colour. Immediately above the centre of the 
top edge of the foot is the mouth, which is the same shape, 
and opens in the same fashion as his salt-water brothers, 
showing the rasping tongue sweeping round the herbage on 
which he browses. To the right and left are the cheeks, 
