. Beginners zoology. Zoology. SPONGES 21 without doubt, many-celled animals. If a living sponge is cut into pieces, each piece will grow and form a complete sponge. That the sponge is not a colony of one-celled animals, each like an amoeba, but is a many-celled animal, will be reahzed by exam- ining Fig. 32, which shows a bit of sponge highly magnified. A sponge may be conceived as having developed from a one-celled animal as follows : Sev- eral one-celled animals happened to live side by side; each possessed a thread-like flagellum (E, Fig. 32) or whip-lash for striking the water. By lashing
. Beginners zoology. Zoology. SPONGES 21 without doubt, many-celled animals. If a living sponge is cut into pieces, each piece will grow and form a complete sponge. That the sponge is not a colony of one-celled animals, each like an amoeba, but is a many-celled animal, will be reahzed by exam- ining Fig. 32, which shows a bit of sponge highly magnified. A sponge may be conceived as having developed from a one-celled animal as follows : Sev- eral one-celled animals happened to live side by side; each possessed a thread-like flagellum (E, Fig. 32) or whip-lash for striking the water. By lashing the water, they caused a stronger cur- rent (Fig. 25) than pro- tozoans living singly could cause. Thus they obtained more food and more rapidly than those living alone. The habit of working together left its impress on the cells and was trans- mitted by inheritance. Cell joined to cell formed a ring; ring joined to ring formed a tube which was still more effective than a ring in lashing the water into a current and bringing fresh food (particles of dead plants and animals) and oxygen. Few animals eat sponges; possibly because spicules, or fibres, are found throughout the flesh, or because the taste and the odour arc unpleasant enough to protect them. Small animals sometimes crawl into sponges to hide. One sponge grows upon shells in- habited by hermit crabs. Moving of the shell from place to place is an advantage to the sponge, while the sponge conceals and thus protects the crab. Special Report: Sponge "; (Localities; how sponges are taken, cleaned, dried, shipped, and sold.). Fig. 32.— Microscopic plan of ciliated chamber. Each cell lining the chamber has a nucleus, a whip-lash, and a collar around base of whip-lash. Question: State two uses of 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 perfe
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1921
