. Animal forms; a second book of zoology. Zoology. 3I0LLUSKS 77 move about, but as they become larger they lose this ability either wholly or periodically. In the edible mussels (Myti- lus, Fig. 47), for example, which are associated in great numbers on the rocks along our coasts, the foot early be- comes long and slender and capable of reaching out a con- siderable distance from the shell to attach threads (byssus), which it spins, to foreign objects. These are remarkably strong, and when several have been spun it becomes a mat- ter of much difficulty to dislodge them. After remaining anchore
. Animal forms; a second book of zoology. Zoology. 3I0LLUSKS 77 move about, but as they become larger they lose this ability either wholly or periodically. In the edible mussels (Myti- lus, Fig. 47), for example, which are associated in great numbers on the rocks along our coasts, the foot early be- comes long and slender and capable of reaching out a con- siderable distance from the shell to attach threads (byssus), which it spins, to foreign objects. These are remarkably strong, and when several have been spun it becomes a mat- ter of much difficulty to dislodge them. After remaining anchored in one situation for a while the mussel may vol-. FlG, 47.—The edible mussel {MytUus edulis), showing the threads by which it is attached. Natural size, from life. untarily free itself, and in a labored fashion move to some other more favorable spot where it again becomes attached, but there are numerous species, such as "fan shells" (Pinna), scallops, Anomia, and a few fresh-water forms, where the union is permanent. Finally, in the oysters, some of the scallops, and a num- ber of less familiar forms, the young in very early life drop down upon some foreign object to which the shell soon becomes firmly attached, and in this same spot they pass the remainder of their lives. The oyster usually falls upon the left half of its shell, which becomes deep and capacious enough to contain the body, while the smaller right valve. 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 Jordan, David Starr, 1851-1931; Heath, Harold, 1868- [from old catalog] joint author. New York, D. Appleton and company
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1902
