Experiments on th^ Respiration of Truncatelta. 301 



it completely with the inclosed animal in a glass of sea- water. 

 For a whole fortnight, I 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, August 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 above 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 I have often thought) dead. I can never see any bubble 

 of air AAHthin 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 crawl 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 



