. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Mesothelium Connective tissue Inner epithelium Figure 25. Holotlmriii forskali. Reconstruction of a longitudinal section through the wall of a stage 5 regenerating Cuvierian tubule (not to scale). BL. basal lamina; BP, epithelial cell basal process: C. cilium; CM. circular myo- cyte; IA, inner area of the connective tissue layer; IE. internal epithelium; GC, granular cell; LM, longitudinal myocyte; M. mesothelium; MV. microvillus; NP. nerve plexus; OA, outer area of the connective tissue layer; P3, type 3 pseudopodial cell;
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Mesothelium Connective tissue Inner epithelium Figure 25. Holotlmriii forskali. Reconstruction of a longitudinal section through the wall of a stage 5 regenerating Cuvierian tubule (not to scale). BL. basal lamina; BP, epithelial cell basal process: C. cilium; CM. circular myo- cyte; IA, inner area of the connective tissue layer; IE. internal epithelium; GC, granular cell; LM, longitudinal myocyte; M. mesothelium; MV. microvillus; NP. nerve plexus; OA, outer area of the connective tissue layer; P3, type 3 pseudopodial cell; PC, peritoneocyte; S. spherule; VC. vacuolar cell. X u TJ C Dfi £ 2. Regeneration stage Figure 26. Labeling indices (mean ± SD. n = 4) for proliferating cells in the different tissue layers at each stage of Cuvierian tubule regeneration (BrdU/anti-BrdU method). (, when the regenerating tubule becomes functional), indicating that the growth phase proceeds only by an in- crease of cell volume, without cell division. Moreover, the absence of DNA-synthesizing cells in non-regenerating Cu- vierian tubules indicates that there is no cellular "turnover" and that the cell populations which constitute the tubule tissues must be considered as static (Messier and Leblond. 1960). During regeneration, the mesothelium is the tissue layer in which cell proliferation is the most precocious and the most important, involving both undifferentiated cells and peritoneocytes. At stage 1. there is an accumulation of actively proliferating undifferentiated cells that form the mesothelial thickening characteristic of this stage. As re- generation proceeds, the percentage of labeled nuclei in the mesothelium regularly decreases in parallel with the differ- entiation of granular cells on the one hand and myocytes on the other hand. Nucleus labeling was never observed in these two cell types, which therefore do not divide. We were not able to determine the origin of undifferentiated cells,
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
