. Elementary zoology. Zoology. BRANCH CCELENTERATA: THE POLYPS, ETC. 99 central stem are many medusoid structures^ the swimming- bells, by means of _ whose opening and closing the whole col- ony is made to swim through the water. Each swimming - bell is a modified medusa- zooid, without tenta- cles, without digestive or reproductive or- gans, but exercising the power of swim- ming by contracting and forcing the water out of the hollow bell just as is done by the free medusae. Be- low the swimming- bells, at the lower end of the central stem, are grouped many structures presenting at first sigh
. Elementary zoology. Zoology. BRANCH CCELENTERATA: THE POLYPS, ETC. 99 central stem are many medusoid structures^ the swimming- bells, by means of _ whose opening and closing the whole col- ony is made to swim through the water. Each swimming - bell is a modified medusa- zooid, without tenta- cles, without digestive or reproductive or- gans, but exercising the power of swim- ming by contracting and forcing the water out of the hollow bell just as is done by the free medusae. Be- low the swimming- bells, at the lower end of the central stem, are grouped many structures presenting at first sight a confu- sion of variety and complexity, but on careful examination revealing themsel ves to be polyp- and me- dusa-zooids modified to form at least five kinds of particularly r . Fig. 14.—A colonial jellyfish (Siphonophora). functioning Struc- (After Haeckel.) tures. There are many flattened scale-like parts whose function is simply that of affording a passive protection, 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. New York : H. Holt and company
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1902
