THE SEA ACORN 119 



sea acorns, and if you put them into a glass 

 vessel of perfectly clean sea-water, you will 

 very soon find that they are swimming about. 

 For though you cannot see the animals them- 

 selves, which are quite as transparent as the 

 water, you will notice little flashes of coloured 

 light, sometimes blue, sometimes green, some- 

 times yellow, and sometimes red, which just 

 gleam out for about half a quarter of a second, 

 and then disappear. You might almost think 

 that a tiny rainbow had been dissolved in the 

 water. 



The fact is this. Running round the oval 

 body of the sea acorn are eight narrow bands, 

 and on each of these are a number of very tiny 

 scales, placed one above another, which keep 

 on rising and falling again, like so many little 

 trap-doors. These scales are really paddles, by 

 means of which the animal drives itself through 

 the water, and as they move up and down they 

 catch the rays of light and break them up, just 

 like that triangular piece of glass which we call 

 a "prism." And though you cannot see the 

 jellyfish itself you can see these little flashes of 

 coloured light, and so can trace the course of 

 the little creature as it travels slowly along. 



This curious jellyfish has only two fishing 

 threads, which hang down from the lower part 

 of its body. But from each of these a number 

 of little side-threads spring out, just like the 



