88 PULMONIFERA.—HELICIDA. 
active a state as when the creature was in motion. 
I would add, also, as adverse to the opinion of the 
French naturalist, that in the Holis and other floating 
species I have distinctly observed the action of the 
foot muscles ; the animal, indeed, literally crawls 
on the under surface of the stratum of air, just as if 
it were a plate of glass. 
The curious habit which these Water-snails have 
of rising perpendicularly through the water, and 
the still more curious power of spimning a thread, 
by the help of which this feat 1s accomplished, 
have been already described in the earlier pages of 
this work. I shall merely add to these particulars 
of their history, that they lay in summer large oval 
masses of clear jelly, which they affix to the stalks 
and leaves of submerged plants. Hach mass con- 
tains from 100 to 130 eggs, which are hatched in 
sixteen days. 
Famity HELIcip&é. 
(Snails.) 
This is an immense family. Between sixty and 
seventy species belonging to it are enumerated as 
natives of the British isles, and those which inhabit 
foreign countries are far more numerous. The tech- 
nical characters may be thus described. The head 
and tentacles are capable of being wholly withdrawn 
into the body, in which state they are covered by 
the infolded skin as with a sheath ; the end of the 
tail tapers to a point, and is destitute of a gland. 
The lung chamber is generally in front of the 
body, with the breathing hole at its hinder part. 
