Experiments on the Respiration of Truncatella. 301 
it completely with the inclosed animal in a glass of sea-water. 
For a whole fortnight, J attended to it with the greatest care, 
changing the water only twice, and then pouring the fresh 
in so as to renew it without pouring off the old, It is 
therefore quite certain, that for the whole time the animal 
never was for a moment in contact with the atmospheric air, 
It did not appear to be suffering the slightest incon- 
venience. Since that time to the present, Jugust 14, 
1827, it has remained in the bag constantly immersed; 
and though I have not attended so particularly to it 
since the first fortnight, I can be very confident that it 
has never been aboye the surface, since the water has 
always been changed by myself, and in the manner before 
described. Sometimes the water has not been changed 
at all for a whole fortnight; once, not for three weeks ; 
and latterly I have never thought of changing it above 
once in a week or ten days. Since the 9th of June, it has 
had no nourishment but what the water afforded. It has 
been perfectly healthy the whole time ; when the water is 
fresh, crawling up to the upper part of the bag, and remain- 
ing there nearly stationary, with its head and body exserted, 
till the water becomes very stale, when it falls generally to 
the bottom, and retreats within its shell, lying apparently 
(as T have often thought) dead. I can never see any bubble 
of air within the aperture now.—Sept. 17. The water was 
changed by another person; and the next day I found the 
animal out of the bag (which had become quite rotten) and 
lying at the bottom of the water. It is alive; and having 
given it fresh sea-water, it begins to craw] as usual, and is 
apparently as strong as ever. It is now left at liberty in the 
water. About the middle of November (exact day not 
noted), I found it lying at the bottom of the water, dead. 
It had for some time previously (since left at liberty), kept 
itself affixed to a cover placed over the glass, out of the 
water for the most part; as Littorina vulgaris usually does, 
This last experiment proves beyond all farther question that the animal 
