. Elementary textbook of economic zoology and entomology. Zoology; Insect pests. CORALS, SEA-ANEMONES AND JELLY-FISHES 65 it settles down, becomes fixed, and develops into a polyp. Thus a polyp may produce a medusa or jelly-fish which, how- ever, produces not a new jelly-fish, but a polyp. This is called an alternation of generations, and is not an uncommon phenom- enon among the lower animals. It results from such an al- ternation of generations that a single species of animal may have two distinct forms. This having two different forms is. FIG. 16.—A jelly-fish, or medusa, Gonionema vertens,
. Elementary textbook of economic zoology and entomology. Zoology; Insect pests. CORALS, SEA-ANEMONES AND JELLY-FISHES 65 it settles down, becomes fixed, and develops into a polyp. Thus a polyp may produce a medusa or jelly-fish which, how- ever, produces not a new jelly-fish, but a polyp. This is called an alternation of generations, and is not an uncommon phenom- enon among the lower animals. It results from such an al- ternation of generations that a single species of animal may have two distinct forms. This having two different forms is. FIG. 16.—A jelly-fish, or medusa, Gonionema vertens, eating two small fishes. (From specimen from Atlantic Coast.) called dimorphism. Sometimes, indeed, a species may appear in more than two different forms; such a condition is called polymorphism. The Portugese man-of-war, common in tropical seas, is a representative of another group of this class. It appears as a delicate bladder-like float, brilliant blue or orange in color, usually about six inches long, and bearing on its upper. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Kellogg, Vernon L. (Vernon Lyman), 1867-1937; Doane, Rennie Wilbur, 1871-. New York, H. Holt and company
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