the Animal and Vegetable Organisms in Sea Water. 323 



sandy bottom ; on the second day after this the oyster was ob- 

 served to have opened the valves of his shell to a great extent, 

 which wei*e afterwards seen closed, but a small Gobius niger, in- 

 habiting the pool, could nowhere be seen. The day after this 

 the oyster was opened for the general feeding, when, lo ! within 

 the shell was found the unfortunate Gobius, quite dead. Whether 

 this little gentleman had been atti-acted within the trap by cu- 

 riosity or the ciliary motion gf the oyster, it is impossible with 

 certainty to say ; but that he must have seized on some sensitive 

 part of the oyster is more than probable, so as to have caused 

 such a rapid closing of the valves of the shell as could entrap so 

 active a burglar. 



Another important point is the gravity of the sea water ; 

 tliis should be very carefully regulated, for it must be borne in 

 mind that many of the marine creatures are suppHed by a per- 

 meation of water through their tissues or over their delicate and 

 beautiful organs. The specific gravity should not rise above 

 1026 at 60" Fahr., and a small hydrometer should be at short 

 periods introduced to ascertain that this point is not exceeded, 

 particularly during the hot months of summer. The reduction 

 to this gravity can be readily effected by the addition of rain or 

 distilled water. i\Iany of the creatures will of themselves aiford 

 indications of this increase of density ; some of the Actinia will 

 remain closed and become coated with a white slimy covering 

 within which they remain for a length of time, and if the specific 

 gravity of the water be lowered this is very soon ruptui'ed bv 

 their expansion, thrown off, and the tentacula become soon 

 extended. 



All putrescent matter or excess of food or rejecta of the Ac- 

 tinicE should be carefully removed from the water, as the noxious 

 gaseous compounds generated by the decay of such matters appear 

 to diffuse themselves rapidly through the water, act as a virulent 

 poison, and speedily destroy the vitality of the occupants. Thus 

 many beautiful subjects were lost in a few hours from the intro- 

 duction, into a small glass jar, of a large Pecten shell, encrusted 

 with corallines, which had become loaded with putrescent matter 

 by partial submersion in a foul muddy bottom. 



Great care should also be taken in moving the Actiniae that 

 the foot or sucking disc with which it attaches itself to the 

 rocks, stones, or mud, be not injured, as, when this occurs, they 

 rarely survive, but roll about without attaching themselves, and 

 gradually waste away and die. 



With these exceptions then, everything has gone on very sa- 

 tisfactorily, care being always taken not to overload the water 

 with too large a proportion of animal hfe for the vegetation to 

 balance, as, whenever this has been inadvertently attempted, the 



