HO ZOOLOGY. 



saucers gradually drop off, and appear as free-swimming 

 medusse. Although originally very small, they soon 

 increase in size, and become, in some cases, of great bulk, 

 measuring seven feet across the disc, with tentacles fifty 

 feet long. These gigantic structures are the sea-blub- 

 bers, sea-nettles, or jelly-fish, so common, in the summer 

 season, round our coasts. 



204. These animals are largely composed of sea water. 



FIG. 58. Aurelia, one of the jelly-fishes. 



Professor Owen has calculated that a jelly-fish, 2 Ibs. 

 weight, does not contain more than 30 grains of solid 

 matter. Some of them are furnished with thread cells, 

 whose barbed points are able to penetrate the humau 



