46 ANIMAL LIFE 



stance. The bodies of all jelly-fishes are soft and gelatinous, 

 the body substance containing hardly one per cent of solid 

 matter. It is mostly water. Many jelly-fishes are beauti- 

 fully and strikingly colored, and as they swim slowly about 

 near the surface of the ocean, lazily opening and shutting 

 their iridescent, umbrella-like bodies, they are among the 

 most beautiful of marine organisms. When one of the 

 jelly-fishes is taken from the water, however, it quickly loses 

 its brilliant colors, and dries away to a shapeless, shrivel- 

 ing, sticky mass. 



Some of the most beautiful of the jelly-fishes belong 

 to a group called the Siphonophora. These jelly-fishes are 

 elongate and tube-like rather than umbrella- or bell-shaped, 

 and they are polymorphic that is, there are several dif- 

 ferent forms of individuals belonging to a single kind 

 or species. The Siphonophora are all free-swimming, but 

 nevertheless form small colonies. In the Mediterranean 

 Sea and in other southern ocean waters the surface may be 

 covered for great areas by these brilliantly colored jelly-fish 

 colonies, each of which looks, as a celebrated German natu- 

 ralist has said, like a swimming flower cluster whose parts, 

 flowers, stems, and leaves seem to be made of transparent 

 crystal, but which possess the life and soul of an animal. 

 An abundant species of these Siphonophora (Fig. 25) is com- 

 posed of a slender, flexible, floating, central stem several feet 

 long, to which are attached thousands of medusa and polyp 

 individuals representing several different kinds of forms, 

 each kind of individual being specially modified or adapted 

 to perform some one duty. The central stem is a greatly 

 elongated polyp individual, whose upper end is dilated and 

 filled with air to form a float. This individual holds up 

 the whole colony. Grouped around this central stem just 

 below the float are many bell-shaped bodies which alter- 

 nately open and close, and by thus drawing in and expelling 

 water from their cavities impel the whole colony through 

 the water. These bell-shaped structures are attached me- 



