4122 Balance between Animal and Vegetable Life. 



shrimps, Nudibranchs, Hololhurias, and some Annelids ; in a second 

 the rock-fish, as the blennies, gobies, Cottus, with crabs and Actiniae; 

 in a third corallines, Annelids, Polyps, rock-borers, Sabellae, Serpulae, 

 Holothurias, and Actiniae. 



Another curious instance of loss I may detail which has quite 

 recently occurred, and which may prove interesting ; it was in a small 

 rock-pool containing blennies, gobies, crabs, &c. I had procured 

 two live oysters for the purpose of feeding my numerous small fry in 

 these vivaria, and one of these having proved ample for the purpose 

 of one meal, the other was placed on the sandy bottom ; on the 

 second day after this the oyster was observed to have opened 

 the valves of his shell to a great extent, which were afterwards seen 

 closed, but a small Gobius niger, inhabiting 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 attracted within 

 the trap by curiosity or the ciliary motion of the oyster, it is impos- 

 sible 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 ; this should 

 be very carefully regulated, for it must be borne in mind that many of 

 the marine creatures are supplied by a permeation of water through 

 their tissues or over their delicate and beautiful organs. The specific 

 gravity should not rise above 1026 at 60 Q Fahr., and a small hydro- 

 meter 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. Many of the creatures will of themselves 

 afford indications of this increase of density ; some of the Actiniae 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 ruptured by their expansion, 

 thrown off, and the tentacula become soon extended. 



All putrescent matter or excess of food or rejecta of the Actiniae 

 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 introduction, into a small 



