SNAILS AND SLUGS 
179 
the common pond snail, a species that is very 
useful as an inmate of an aquarium because it 
feeds upon rotting vegetation, thereby keeping 
the water from becoming stale. Although it 
spends much of its time crawling about in the 
usual snail-like fashion, it frequently comes to 
the surface to breathe, when it often floats in 
an inverted position. 
Notwithstanding that the water snails are 
aquatic in habits, most of them will drown if 
submerged beneath the water for too long a 
time. This, however, does not apply to a water 
snail found in Madagascar, which possesses 
gills that enable it to extract the air held in 
the water. 
The ramshorn snail and the viviparous pond 
snail are other species to be met with in this 
country, the former inhabiting stagnant pools 
and ditches, and the latter selecting the mud- 
bed for its habitation. The ramshorn snail, 
which has the curious habit of ejecting a purple- 
coloured fluid when alarmed, receives its name 
from the flattened and tightly-coiled nature of 
its shell; while the viviparous snail, as implied 
by its name, is so called on account of the fact 
that its young are brought forth in a fully 
developed state, instead of being hatched from 
eggs laid by the female. 
Very curious are the amphibious snails or 
