. A textbook in general zoology. Zoology. MUSSELS, CLAMS, OYSTERS, SNAILS, SQUIDS 105 lAciatMre the scar of the protractor muscle of the foot; just above the posterior adductor muscle scar is the small scar of the posterior retractor foot muscle; parallel with the edge of the valve and a short distance from it is a delicate streak, the pallial line, that marks the hne along which the mantle lobe is joined to the shell (Fig. 54). How the mussel opens and shuts its shell. — The anterior adductor muscle and the posterior adductor muscle run straight across the cavity between the valves, and their
. A textbook in general zoology. Zoology. MUSSELS, CLAMS, OYSTERS, SNAILS, SQUIDS 105 lAciatMre the scar of the protractor muscle of the foot; just above the posterior adductor muscle scar is the small scar of the posterior retractor foot muscle; parallel with the edge of the valve and a short distance from it is a delicate streak, the pallial line, that marks the hne along which the mantle lobe is joined to the shell (Fig. 54). How the mussel opens and shuts its shell. — The anterior adductor muscle and the posterior adductor muscle run straight across the cavity between the valves, and their ends are fastened firmly to the inside walls of the shell (Fig. 55). Therefore, when they contract and shorten, the valves are pulled together and held tightly closed. On the other hand, whenever the ad- ductor muscles are relaxed, the strong hinge ligament, which all the time the valves are closed is tightly stretched, throws the shell open by its elasticity. Thus the shell is closed with muscular effort, but is opened by a me- chanical, springlike action which requires no effort on the part of the animal, is open much more than it is shut, this is a striking adap- tation to the mussel's mode of living. The mantle and siphons. —Lining the inside of both valves and completely enveloping the body is a soft, white, delicate membrane known as the mantle. It really consists of two lobes corresponding to the valves. The ventral edges of the mantle lobes are free and run parallel with the. Fig. 55. —Cross section of mus- sel, showing mechanism of opening and closing. Since 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 Herrick, Glenn W. (Glenn Washington), 1870-1965. New York, Cincinnati [etc. ] American Book Company
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
