164 AMERICAN JOURNAL 



" I noticed in the last Report, that living Mollusca, taken by 

 the dredge from considerable depths, and placed in a shallow 

 vessel of water drawn from the shore, did not appear to be in 

 the slightest degree affected by the sudden change of bathy- 

 metrical conditions. I wish to qualify this statement, and, at 

 the same time, to record a further observation. It is quite 

 true that the Mollusca in question were lively and active in 

 their new habitat; but those which were of the univalve kind 

 exhibited a peculiarity and habits with which I was much 

 struck. All of them, on being placed in the vessel, tried to 

 escape from the bottom, and quickly found their way up the 

 sides to the open air; some floated with the sole of the foot 

 uppermost and the shell downwards. Now, it is very certain 

 that in their native habitat, at a depth of nearly 500 feet, these 

 raollusks, which are ground-dwellers and have no means of 

 rising to the surface of the sea, could not have floated in this 

 way, or even had time or opportunity, since they were taken 

 up from the depths of the ocean, to acquire such a habit. 

 Was it instinct? If so, when was it implanted? Another 

 fact worthy of notice is the eagerness which they displayed to 

 escape out of the water and to breathe the open air. One 

 would have supposed that the water at the bottom of the 

 ocean was much less aerated or oxygenated than that on the 

 shore, and that the mollusks would have supplied their gills 

 more copiously in surface- water with the requisite element. 

 But exactly the contrary has been ascertained by some ex- 

 periments conducted on board the French surveying ship 

 'Bonite;' and it is now clearly established that the quantities 

 of atmospheric air increase with the depth. According to Dr. 

 Wallich, in an admirable chapter of his 'North Atlantic Sea 

 Bed,' entitled 'The Bathymetrical Limits of Life in the Ocean,' 

 the proportion of gaseous matter taken up by water is very 

 greatly increased under an increase of pressure, all gases (es- 

 pecially oxygen and hydrogen) being easily compressible and 

 becoming liuid under a comparatively slight pressure. We 

 but imperfectly understand the mode in which the solution of 

 atmospheric air in sea-water is brought about; but the ten- 

 dency of fluids to absorb gaseous bodies is constant under all 

 circumstances, and the quantity which they are capable of 

 appropriating increases with pressure. It, therefore, follows 

 that the deeper the stratum of water, the greater must be the 

 amount of gaseous matter held in solution by it. For a more 

 detailed explanation of this problem I must refer to the work 

 above cited. I can now understand why deep-water mollusks 

 do not find in the surface-water the same supply of atmos- 

 pheric air as they had been accustomed to, and why they 



