. Essentials of biology presented in problems. Biology. XXI. THE MOLLUSKS Jfroblem XXXIII (Optional). ,1 study ofmollusks and their enemies with reference to their economic importance. {LaJjora- tory Manual, Prob. AWWIII.) To the a\erage high, school pupil a clam or oyster on the " half shell" is a familiar object. The soft " body " of the animal lying between the two protecting " valves " of the shell gives the name to this group (Latin mol- lis— soft). iMost have a limy shell, either bivalve (two-vahed), as the oyster, clam, mussel, and scallop, or uni
. Essentials of biology presented in problems. Biology. XXI. THE MOLLUSKS Jfroblem XXXIII (Optional). ,1 study ofmollusks and their enemies with reference to their economic importance. {LaJjora- tory Manual, Prob. AWWIII.) To the a\erage high, school pupil a clam or oyster on the " half shell" is a familiar object. The soft " body " of the animal lying between the two protecting " valves " of the shell gives the name to this group (Latin mol- lis— soft). iMost have a limy shell, either bivalve (two-vahed), as the oyster, clam, mussel, and scallop, or univalve, as in the snail. Usually the univalve shell is spiral in form, some of nature's most beautiful objects being the spiral shells of some marine forms. StiU other mollusks, for example, the garden slug, have no external shell whatever. This limy shell envelope when present, is formed from the outer edge and surface of a deUeate body co-iering called the mantle. The mantle may be found in the opened oyster or clam sticking close to the inside of the valve of the shell in which the body rests. Between the mantle and the body of the clam or oyster is a space, the mantle cavity. In the space hang the gills, platelike striated structures. By means of cilia on the inner surface of the mantle and on the gills a con- stant current of water is maintained through the mantle cavity bearing oxygen to the gills and carbon dioxide away. This current of water passes, in most mollusks, into and out from the mantle ca\'ity through the siphons, the muscular tubes forming the "neck"of the "soft clam" being an example of such an organ. The food of clams or oysters consists of tiny organisms, plant and animal, which are carried in the ctirrent of water to the mouth of the animal, this water current being maintained in part by the action of cilia on the palps or liplike flaps (p. 269) surrounding the mouth. A single muscular foot aids in locomotion when the animal moves abo
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbiology, bookyear1911
