Beginners' zoology . bCLliuU of horny sponge. SPONGES 21 without doubt, many-celled animals. If a living sponge is cutinto pieces, each piece will grow and form a complete sponge. That the sponge is not a colony of one-celled animals, each likean amoeba, but is a many-celled animal, will be realized by exam-ining Fig. 32, which shows a bit of sponge highly magnified. Asponge may be conceived as having developed from a one-celledanimal as follows : Sev-eral one-celled animalshappened to live side byside; each possessed athread-like fiagellura (E,Fig. 32) or whip-lash forstriking the water. Byla
Beginners' zoology . bCLliuU of horny sponge. SPONGES 21 without doubt, many-celled animals. If a living sponge is cutinto pieces, each piece will grow and form a complete sponge. That the sponge is not a colony of one-celled animals, each likean amoeba, but is a many-celled animal, will be realized by exam-ining Fig. 32, which shows a bit of sponge highly magnified. Asponge may be conceived as having developed from a one-celledanimal as follows : Sev-eral one-celled animalshappened to live side byside; each possessed athread-like fiagellura (E,Fig. 32) or whip-lash forstriking the water. Bylashing the water, theycaused a stronger cur-rent (Fig. 25) than pro-tozoans living singlycould cause. Thus theyobtained more food andmultiplied more rapidlythan those Hving habit of workingtogether left its impresson the cells and was trans-mitted by inheritance. Cell Joined to cellformed a ring; ring. Fig. 32.— Microscopic plan of ciliated cell lining the chamber has a nucleus,a whi[>lash, and a collar around base ofwhip-lash. Question: State two uses ofwhip-lash. joined to ring formed a tube which was still more effective thana 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 areunpleasant enough to protect them. Small animals sometimescrawl into sponges to hide. One sponge grows upon shells in-habited by hermit crabs. Moving of the shell froin place to placeis an advantage to the sponge, while the sponge conceals and thusprotects the crab. Special Report: Sponge Fisheries.^ (Localities; how spongesare taken, cleaned, dried, shipped, and sold.) CHAPTER IV POLYPS (CUPLIKE ANIMALS)
Size: 1467px × 1703px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1921
