. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. No. 6.] THE LIMBS OF PLETHEDON. 295 the first place there is a great increase in the number of nuclei zvit/iin the old fibers, but in no case is any karyokinesis found there. This degenerative process in the old fibers must there- fore take place by direct division of the nuclei. Instances of this division are shown in Figs. 5 and 6. To this division and to the disintegration of some of the old fibers is due the enor- mous accumulation of nuclei in the outer part of the limb (Fig. 2). The cells so formed then begin to divide
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. No. 6.] THE LIMBS OF PLETHEDON. 295 the first place there is a great increase in the number of nuclei zvit/iin the old fibers, but in no case is any karyokinesis found there. This degenerative process in the old fibers must there- fore take place by direct division of the nuclei. Instances of this division are shown in Figs. 5 and 6. To this division and to the disintegration of some of the old fibers is due the enor- mous accumulation of nuclei in the outer part of the limb (Fig. 2). The cells so formed then begin to divide by karyo- kinesis in the region of the cut, and thus a further increase in their number takes place. In these outer cells new muscle tissue forms and the new fibers are built up. A certain. FIG. 5. FIG. 6. number of the old fibers remain in the middle of the limb, and in these the muscle tissue never disintegrates, though it splits longitudinally. Again, as at any one level the number of nuclei far exceeds the number of fibers in a normal muscle, a great number of them must, between the early stages and the fully formed limb, either degenerate or be transported (cf. Figs. 3 and 4). That this is so is easily seen, for two reasons: (i) when the new fibers form, at a given level several nuclei are often included in one fiber ; when the limb is full-grown there is only one ; (2) among the newly formed fibers, but between them, are many scattered nuclei; the majority of these disappear in later 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 Marine Biological Laboratory (Woods Hole, Mass. ); Marine Biological Laboratory (Woods Hole, Mass. ). Annual report 1907/08-1952; Lillie, Frank Rattray, 1870-1947; Moore, Carl Richard, 1892-; Redfield, Alfred Clarence, 1890-1983. Woods Hole, Mass. : Marine Biologica
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