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 “snoods” on the lines which fishermen use in the sea. And the animal is always throwing these out and drawing them in again, so that it really “fishes” for the tiny little creatures on which it feeds.