. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 206 R. S. McCURLEY AND W. M. K1ER \. Figure 9. Photomicrograph of a transverse section of the radial canal (R) of Luiclia clathrata. The connective tissue (CT) of the ambulacrum surrounds the radial canal. No muscle fibers encircle the radial canal. The section is slightly oblique and includes a portion of the valve (V) on the left side of the figure. The radial nerve (N) is located in the center, between the two tube feet (T). Scale bar, 100 ^m. A \-nm- thick glycol methacrylate section stained with Lee's methylene blue-bas
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 206 R. S. McCURLEY AND W. M. K1ER \. Figure 9. Photomicrograph of a transverse section of the radial canal (R) of Luiclia clathrata. The connective tissue (CT) of the ambulacrum surrounds the radial canal. No muscle fibers encircle the radial canal. The section is slightly oblique and includes a portion of the valve (V) on the left side of the figure. The radial nerve (N) is located in the center, between the two tube feet (T). Scale bar, 100 ^m. A \-nm- thick glycol methacrylate section stained with Lee's methylene blue-basic fuchsin and photographed under bnghtlield illumination. Tube foot bending. Bending of the tube foot involves the same musculature as that used for elongation and shortening. During bending, however, the longitudinal muscles of the tube feet and the circumferential muscles of the ampullae operate synergistically rather than antagonistically. Bending of a hydrostatic structure re- quires unilateral longitudinal muscle contraction on the inside radius of the bend. The force of this contraction not only bends the structure, but also tends to decrease its length. For bending without shortening, the longitu- dinal compressional force must be opposed by a resistance to expansion of the ampulla, which prevents displacement of the fluid from the tube foot. Expansion of the ampulla is resisted by contractile activity of the circumferential muscles. Thus, bending requires simultaneous unilateral longitudinal muscle contraction of the tube foot and cir- cumferential muscle contraction of the ampulla. Gener- ation of a localized rather than a more generalized bend is dependent on the degree to which the pattern of activity of the longitudinal musculature of the tube foot is local- ized. No morphological subdivision of the longitudinal musculature at the base of the tube foot was observed in the species examined in this study. The role of the radial canal. There is no evidence in the spec
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
