328 EARTH TEESPASSEES. 



How they find their way to the water is not known . 

 Their eyes being so close to the ground, they have but 

 little range of vision ; so that they cannot guide them- 

 selves by sight. Perhaps their sense of smell may 

 have something to do with it ; or they may possess a 

 sense which is unknown to us, by which they are 

 guided to the water. 



This seems to be the case with the Crustacea, as 

 regards their food. If a number of shrimps and 

 prawns are in a tank, and a tiny piece of meat be 

 gently fplaced in the water and allowed to sink, the 

 creatures take no notice for some little time. But if 

 one of them happens to swim across the track of the 

 meat, it becomes all life and animation ; waves its 

 antennae here and there, like a dog hunting by scent, 

 and then, having got on the track, follows it up, and 

 seizes its food. A piece of shrimp or prawn will do 

 just as well as any meat, the Crustacea being terrible 

 cannibals. 



If the water were quite still, there would be little 

 difficulty in understanding that the scent might be left 

 in it. But at the Crystal Palace aquarium the water 

 is perpetually driven through the tanks by a steam- 

 engine, spirting into them with such force that the 

 water is divided into a number of currents, crossing 

 each other in all directions, as may be seen by the 

 myriads of tiny air-bubbles which sparkle in it like 

 those of newly-opened soda-water. Not a drop of 

 water remains still for a second. The tiny column of 

 water through which the piece of food passed, and in 

 which its scent might have remained, was dispersed 

 over the entire tank before it escaped at the outlet . 



