General remarks. 



39 



from the water, the fixed animals by driving the water through 

 their bodies, the whales by driving their bodies through the water. 

 Tlius no inhabitant of the aquarium needs to undertake a tiring 

 hunt for booty. Each gets his full share, and even if the hermit- 

 crabs in tank 23 do scuffle for their mouthfuls, this is only a game 

 without which the food has no taste for these odd little beasts. 



Not only in the air and sunlight does respiration go on, but 

 down below too, in the water, everything breathes. The only 

 animal in the Aquarium which has to poke its nose above the 

 surface to take in air is the turtle. All others, whether they have 

 true gills like fish, molluscs and custaceans, or not, extract their 

 air from the water, without which air they could not continue to 

 live. For this reason a stream of clean oxygen-containing water 

 is continuously driven into the tanks and the used-up water led 

 off. The pumps must work steadily, with a short intermission 

 during the night hours so that the water will stream into the tanks 

 with enough force to take up the greatest possible quantity of air 

 in the finest bubbles. This spray of air and water is best seen 

 in tank 10 where the Sea-Perch delight in allowing their gills to 

 be sprayed by the stream. The water is not pumped directly from 

 the Gulf into the Aquarium tanks and the reason will be well- 

 known to those who have been to Capri. The famous ultramarine 

 blue of the Mediterranean is to be seen only at some distance 

 from the harbour. Further in, the water is green or yellow in colour, 

 a sign of impurity which would be very harmful to the inhabitants 

 of the aquarium. For this reason the water is first allowed to 

 stand in large cisterns in the cellars until it becomes clear, after 

 which it is led into the tanks. 



The greatest difficulties are encountered in avoiding extreme 

 temperatures, the third of the three conditions mentioned above. 

 For in this respect the inhabitants of the Bay are much less used 

 to changes of temperature than their neighbours on land. When 

 the land-temperature falls to o^ C and below and lizards creep 

 into their holes and men under the bed-clothes in their unheated 

 rooms, the sea-water is still at least at 12^/2^ C. x^nd when in 

 summer the Scirocco compels us for days on end to take an un- 

 willing steam-bath, at 30 ^ C or more in the shade, the lucky dwel- 

 lers in the Bay, if they are not fixed to the cool ground, need 

 only to dive a few yards down from the surface, which is never 

 above 27 ^ C, to reach the region of even temperature. For not 

 only in the Bay of Naples, but throughout the whole Mediter- 

 ranean, the water is never warmer than 27 ^ C nor colder than 

 13 C. And further, these extremes are only met with in the 

 surface layers. At depths lower than 500 metres all variations 

 cease and from there down to the sea-bottom there is an even 

 temperature of 13 ^ C the whole year through. 



