. Animal biology. Zoology; Biology. 134 METAZOAN PHYLA animals and man, such as the muscle which shuts Oif the stomach from the intestine, that which guards the exit from the bladder, and that which controls the passage of egested matter from the posterior end of the alimentary canal.) 158. Reproduction.—Reproduction is both sexual and asexual. The asexual mode of reproduction involves the gradual formation of external buds which arise near the point of attachment of the parent. After grow- ing for a time thus attached a bud may separate and begin an individual .'•';6V-Vffifb; jr:0 ci. B Fi
. Animal biology. Zoology; Biology. 134 METAZOAN PHYLA animals and man, such as the muscle which shuts Oif the stomach from the intestine, that which guards the exit from the bladder, and that which controls the passage of egested matter from the posterior end of the alimentary canal.) 158. Reproduction.—Reproduction is both sexual and asexual. The asexual mode of reproduction involves the gradual formation of external buds which arise near the point of attachment of the parent. After grow- ing for a time thus attached a bud may separate and begin an individual .'•';6V-Vffifb; jr:0 ci. B Fig. 56.—Gemmules of a fresh-water sponge, Carterius tubisperma Mills. A, fragments of old sponge and gemmules on a piece of wood. X about 3. B, section of a gemmule showing arrangement of spicules in the shell, the foraminal tubule, and the many enclosed cells which were separated from the tissues of the old sponge. X 78. {Drawn by E. F. Powell.) existence. If budding continues and the individuals remani together, a colony is produced (Fig. 53 A). In addition to external budding, some sponges have the ability to form gemmules, or internal buds. These are groups of cells which gather together in the middle layer and become surrounded by a siliceous shell. They are formed when living conditions become difficult and thus preserve the life of the organism during such periods. The gemmules are produced in the autumn, after which the adults die; in the spring the growing cells of the gemmule escape from the shell. 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 Wolcott, Robert Henry, 1868-1934; University of Nebraska (Lincoln campus). Dept. of Zoology. New York ; London : McGraw-Hill Book Company, Inc.
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Keywords: ., bookcentury1900, bookcoll, booksubjectbiology, booksubjectzoology
