. A text-book of invertebrate morphology. Invertebrates. 20 INVERTEBRATE MORPHOLOGY. spicules, while in TJmlassicoUa, already alluded to (Fig. 7), it is entirely absent. As stated, it is usually siliceous in char- acter, though in AcantJiometra it is composed of a peculiar horny material termed acanthin. Scattered through the protoplasm of the Eadiolarians there are usually to be seen numbers of small yellowish bodies long known as the "yellow ; They are not con- stant, however, individuals of any species frequently being destitute of them, a peculiarity due to the " yello
. A text-book of invertebrate morphology. Invertebrates. 20 INVERTEBRATE MORPHOLOGY. spicules, while in TJmlassicoUa, already alluded to (Fig. 7), it is entirely absent. As stated, it is usually siliceous in char- acter, though in AcantJiometra it is composed of a peculiar horny material termed acanthin. Scattered through the protoplasm of the Eadiolarians there are usually to be seen numbers of small yellowish bodies long known as the "yellow ; They are not con- stant, however, individuals of any species frequently being destitute of them, a peculiarity due to the " yellow cells " not being really constituent parts of the Eadiolarian, but. Pig. 8.—Helios'pUcen'a actinota (after Haeckel from Hatschek). foreign bodies, in fact unicellular plants, for which the term Zooxantkellce has been proposed. They cannot be consid- ered parasites, since they do not appear to exist at the ex- pense of the host, but, on the contrary, their presence seems actually to be beneficial. Mutual benefits ai'e conferred br the plant and the Eadiolarian, the coexistence constituting an example of the phenomenon known as Symbiosis. Beproduction in the Rhizopods.—Throughout all the groups the simplest form of reproduction, fission, is probably preva- lent (Fig. 9), though it is not yet definitely known to occur in. 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 McMurrich, J. Playfair (James Playfair), 1859-1939. New York, H. Holt and Company
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