ON GASTEROPODA. 347 
many other zorms, but the sexes are separated in different 
individuals. 'This, however, is indicated by no external dis- 
similarity. The anus and sexual organs are placed in a com- 
mon cloaca at the hinder extremity of the tail, and during in- 
tercourse the distinction of sex is very evident. This animal 
lives on the leaves of the typha elephantina, common on the 
banks of the Ganges. 
The manners and habits of the PLANORBES are nearly the 
same with those of the next genus, (Limnee) with which they 
are constantly found. Thus they are fresh-water animals, 
altogether aquatic, perhaps more so than the limnee. In fact 
they are very seldom indeed to be met with out of the water. 
They crawl, like them, on the surface of bodies as well as on 
that of the water, with the foot upwards, and the shell down- 
wards. They equally feed upon vegetable substances, which 
they eat in the same manner. Their mode of sexual inter- 
course is exactly similar: the individuals form long lines, be- 
ginning with a male, and ending with a female; but they are 
hermaphrodite. The eggs which they lay are in a gelatinous 
mass, applied against submerged bodies. In our temperate 
climates, and in cold climates, the planorbes, at the approach 
of winter, sink into the mud, and fall into a lethargic state, so 
that it is impossible to find an individual in a place where, 
some months before, there were myriads. 
The species of this genus appear rather to belong to the 
temperate and boreal zones, than to the other parts of the 
world. They are very common in Europe and North America. 
Few are known in the Austral regions ; many are found in the 
fossil state. 
A viscous matter issues from the collar of these animals, 
when it is irritated. 
The Limna appear to possess a greater degree of sensi - 
bility than most other mollusca, which is doubtless owing to 
their skin being more gelatinous and less tuberculous. ‘They 
