TROCHUS. 335 



the Scheld near Antwerp (De Wael). It has been 

 taken on many parts of the Scandinavian coast, as far 

 north as Havosund, at depths varying from 25 to 150 f. 

 (Loven and others) ; and off Grand Manan and Casco 

 Bay, in Maine, at 30 f. and more (Mighels and 

 Stimpson) . 



Although an inhabitant of the deep-sea zone, its first 

 impulse, when taken from it and placed in a vessel of 

 water, is to crawl out into the open air, or to float with 

 the sole of the foot uppermost and the shell downwards. 

 The eagerness thus shown to get to the surface, appa- 

 rently for the purpose of respiration, does not accord 

 with the general notion that the water at the bottom of 

 the sea is less aerated or oxygenated than that on the 

 shore. However, exactly the reverse has been ascer- 

 tained by means of some experiments conducted on 

 board the French surveying-ship ' Bonite ' ; and it is 

 now a recognized fact that the quantity of atmospheric 

 air increases with the depth of water. According to 

 Dr. Wallich (' North Atlantic Sea-bed/ p. 120), " hy- 

 drogen and oxygen, both of which gases in their separate 

 state resist all pressure that has been applied to them, 

 when combined to form water continue liquid under a 

 pressure considerably below that of a single atmo- 

 sphere." We do not yet exactly understand the mode 

 in which the solution of atmospheric air in sea-water is 

 brought about ; but the tendency of fluids to absorb 

 gaseous matter is constant under all circumstances, and 

 their capability of appropriating it is facilitated by the 

 pressure of the overlying stratum. This may account 

 for deep-sea mollusks not finding in water drawn from 

 the surface of the ocean a supply of oxygen equal to that 

 which they had been accustomed to enjoy, and for their 

 escaping into the open air to avoid a sensation which 



