Image from page 154 of "The origin and evolution of life, on the theory of action, reaction and interaction of energy" (1917)
Authors: Osborn, Henry Fairfield, 1857-1935
Publisher: New York, C. Scribner's Sons
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library
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protoplasm contain-ing a nucleus within which lies the heredity-chromatin(Fig. 12). This passes into the plasmodial condition ofthe Rhizopods, in which the protoplasm increases enormouslyto form the relatively large, unprotected masses adapted to Jennings, H. S., 1906, pp. 318, 319. . Op. cit., pp. 329-335- ^ These two explanations are fully set forth below (see pp. 143-146) in the introduc-tion to the evolution of the vertebrates. ■* Adaptive radiation—the development of widely divergent forms in animals ances-trally of the same stock or of related stocks, as a result of bodily adaptation to widelydifferent environments (see p. 157). ^ Minchin, E. A., 1916, p. 277. EVOLUTION OF PROTOZOA 115 the creeping or semiterrestrial mode of life. From theseevolve the forms specialized for the floating pelagic habit,namely, the Foramiiiijera and Radiolaria, protected by anexcessive development and elaboration of their skeletal struc-tures.^ Less cautious observers- than Jennings find in the
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Fig. 18. Skeletons of Typical Protozoa. B. Siliceous skeleton or shell of a typical radiolarian, Stauraspis siaiiracantha Haeckel, 170 times the actual size. Owing to their vast numbers, these microscopic, glassyskeletons are an appreciable factor in earth-building. A large part of the islandof Barbados is formed of radiolarian ooze. Photographed from a model in theAmerican Museum. C. Calcareous skeleton or shell of a typical foraminifer. Globigcnna bidloidc; dOrbigny, 30 times the actual size. As the animal increases in size it forms successivelylarger shells adjoining the earlier ones until, as shown in the figure, a cluster ofshells of increasing size is formed. The name foraminifer refers to the manyminute openings, plainly seen in this figure, through which the pseudopodia canpass. Photographed from a model in the American Museum. (Compare Fig. i6,p. 112.) Foraminifera the rudiments of the highest functions and themost intelligent behavior of which undifferentiated protoplasmhas
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