Page:Popular Science Monthly Volume 16.djvu/662

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—a true individual of a higher order. Here the transformation of the colony to an individual is manifest. The Siphonophore is an PSM V16 D662 Portuguese man of war.jpgFig. 8.a, Portuguese man-of-war (after Huxley); b, Velella vulgaris (after Gosse). animal with organs made up of distinct animals, each having a particular function. Elsewhere we see these animal organs become less and less independent. They come together and arrange themselves around a central axis which predominates, and end by forming a being like the Porpita or Velelle, which, but for the study of neighboring types, would not be thought of as a decomposable animal.

At the present time most people consider Sea-anemones (Fig. 9) and Polyps, of the madrepores, and coral, as simple organisms—primitive individuals; while to us their origin is the same as that of Porpitæ and Velellæ—the union of three sorts of Hydroid Polyps. The admirable researches of Moseley on the Polyps of the family of Stylasteridæ furnish proof of this. If we consider only their calcareous parts, all these beings seem to be true Madrepores. The first doubt concerning their true nature was raised by Agassiz, with reference to the Millepores.

PSM V16 D662 Sea anemones.jpg
Fig. 9.—Sea-Anemones. a, Actinia rosea; b, Arachnactis albida (after Gosse).

Between a Coralarian and a Hydroid Polyp the difference is considerable. One is a simple sac with tentacles, usually solid appendages