314 Mr. R. Warington on the Aquarium. 



continued flux and reflux of the tides, and by the enormous 

 streams of water which must be flowing from the Arctic regions 

 from year's end to year's end in one constant current, and 

 which, by their movement, must necessarily cause other currents 

 to flow in and take their place, thus forcing, as it were, the 

 heated surface-water of the tropical seas towards the colder 

 regions of the globe. Again, the whole surface of the earth, 

 submersed below the ocean, is protected by this fluid coating 

 from the efi'ects of the cooling influences of radiation on the one 

 hand, and from contact with the currents of the atmosphere on 

 the other ; and hence we perceive an always existent cause for 

 the maintenance of a steady, equable temperature by the waters 

 of the ocean throughout the year. 



Many of the inhabitants of the sea are very sensitive to 

 changes of temperature, and we find that a few degrees of 

 variation will cause them rapidly to move their position and 

 seek some cooler or warmer spot as the case may be. In the 

 ocean it will be evident that the creatures have the power 

 readily to efi^ect this under ordinary circumstances, by seeking 

 deeper water not liable to be aff'ected by atmospheric influ- 

 ences, by partially or entirely burying themselves in the sand 

 or shingle, or by shielding their bodies under the protecting 

 shadow of the rocks or growing vegetation. In arranging the 

 rock-work in the interior of the aquarium, therefore, great care 

 should be taken to keep these points in view, and to aff'ord as 

 much protection as possible to the creatures from the cooling 

 influences of radiation on the one hand, and from the heat of 

 the sun's rays on the other. 



From my own experience I find that the range of tempe- 

 rature should not be below 50° Fahr., nor above 70° ; within 

 these limits all appears to progress healthily, but beyond these 

 points many of the creatures are rapidly affected. During 

 the last long-continued and severe winter, it was found very 

 difficult, in an ordinary sitting-room having a south aspect 

 and a good fire maintained throughout the day — the tanks being 

 also screened at night by a blind, — to prevent the powerful 

 cooling efi'ects from radiation on a clear frosty night ; and 

 on three several occasions, marking exactly the three severest 

 frosts that we experienced during the winter, the thermometer, 

 immersed in an aquarium containing about thirty gallons of 

 water, fell as low as 45° Fahr. The Shrimp and Crab tribes, 

 and the Crustaceans generally, are especially aff'ected by these 

 changes, and on each of the three occasions alluded to, one 

 or two individuals perished ; the larger-sized Prawns, as Pal<2- 

 mon serratuSj appeared to suff'er more readily than the P. squilla, 

 although this might arise from the smaller ones being able 



