. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HOLOTHUROID CUVIERIAN TUBULE REGENERATION 43 MV. Figure 2(1. Holothuriu frrxkuli. Reconstruction of a longitudinal sec- tion through the wall of a stage 4 regenerating Cuvierkm tubule (not to scale). BL. basal lamina; BP. epithelial cell basal process; C, cilium: CL. connective tissue layer; CM. circular myocyte; IE. internal epithelium; GC. granular cell; LM, longitudinal myocyte; M. mesothelium; MV. microvil- lus; NP, nerve plexus; P3. type 3 pseudopodial cell; PC. peritoneocyte: SG, secretory granule. mesothelium. prolife
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HOLOTHUROID CUVIERIAN TUBULE REGENERATION 43 MV. Figure 2(1. Holothuriu frrxkuli. Reconstruction of a longitudinal sec- tion through the wall of a stage 4 regenerating Cuvierkm tubule (not to scale). BL. basal lamina; BP. epithelial cell basal process; C, cilium: CL. connective tissue layer; CM. circular myocyte; IE. internal epithelium; GC. granular cell; LM, longitudinal myocyte; M. mesothelium; MV. microvil- lus; NP, nerve plexus; P3. type 3 pseudopodial cell; PC. peritoneocyte: SG, secretory granule. mesothelium. proliferating cells are present from regenera- tion stage 1 to stage 4. In all these stages, labeled nuclei were always observed in undifferentiated cells and perito- neocytes (Figs. 30. 31). No labeling was detected in myo- cytes and granular cells, whatever the regeneration stage considered. Labeled cells were observed in the connective tissue layer until the regenerating tubule becomes a small functional tubule (, end of stage 5). These cells were always pseudopodial cells (Figs. 30, 31) and never spheru- locytes. Among the three types of pseudopodial cells, la- beled nuclei were observed principally, but not exclusively, in type 2 cells (Figs. 29-31). As for the inner epithelium, the labeling was always detected in epithelial cells that had not yet developed piles of spherules in their intraconnective basal processes. Discussion Echinoderms in general, and holothuroids in particular, exhibit a remarkable ability to regenerate a missing part of the body (Hyman. 1955). Regeneration in echinoderms gen- erally occurs after evisceration, autotomy, or fission (Emson and Wilkie, 1980). In sea cucumbers, the best studied re- generative model is the intestine regeneration after eviscer- ation (Dawbin, 1949; Mosher. 1956; Bai. 1971; Tracey, 1972; Garcia-Arraras et al., 1998). In this model, formation of the new gut may be subdivided into three successive phases: initial repair, true reg
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