. The biology of the Protozoa. Protozoa; Protozoa. STRUCTURAL DIFFERENTIA TIONS 131 such skeletons have theu- beginnings in spicules which conform in shape and size with the nodal points in the alveolar walls of the cyto- plasmic reticulum (Fig. 11, p. 33). Isolated spicules are character- istic of several Heliozoa and Radiolaria where they form a loose or felted covering in the outer protoplasm. Such spicules invari- ably grow by accretion, that is, by the addition of new substance to the outside of that already formed. If such added material is formed in a limited region of the protoplasm, t
. The biology of the Protozoa. Protozoa; Protozoa. STRUCTURAL DIFFERENTIA TIONS 131 such skeletons have theu- beginnings in spicules which conform in shape and size with the nodal points in the alveolar walls of the cyto- plasmic reticulum (Fig. 11, p. 33). Isolated spicules are character- istic of several Heliozoa and Radiolaria where they form a loose or felted covering in the outer protoplasm. Such spicules invari- ably grow by accretion, that is, by the addition of new substance to the outside of that already formed. If such added material is formed in a limited region of the protoplasm, the result is a con- tinued accretion of silica to the end of a spicule which is pushed. Fig. G7.—Types of spicules in Heliozoa. ^4, Raplndiophrys pallida with curved silicious spicules; B, Pinaciophora ruhiconda with tangential plates and forked spines; C, Acanthocystis turfacea, with separated plates and forked spines; D, Pinaciophora fluviatilis. (From Calkins after Penard.) farther out with each increment, thus giving rise to long bars and spines which are radially arranged in forms like Acanthocystis acvleata, etc. (Fig. 67). The silicious deposit, again, may be made throughout a zone completely surrounding the center, resulting in clathrate or latticed skeletons of varying grades of complexity {Clathrulina elegans, NasseUario). Cellulose mantles are limited almost entirely to forms provided with chlorophyll, and able to form starch by virtue of the energ^>' of the sun's rays. Cellulose is a by-product of these cells and is secreted either as a uniform covering for the entire organism, as in man\'. 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 Calkins, Gary N. (Gary Nathan), b. 1869. Philadelphia, New York, Lea & Febiger
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