PCNA was used as a measure of cell proliferation. A. At ED4 (i-i’) and ED6 (ii-ii’) all nuclei of the epithelium and central fiber cells were positive for PCNA. B. Quantification of the percentage of PCNA positive nuclei revealed a progressive reduction in PCNA labeling in the central epithelium, peripheral epithelium and central fiber cells as development proceeded. Error bars represent the standard error of the mean. Statistical significance was determined for all groups with respect to ED 4 (*=p<0.05). To access the data, click or select the words “Appendix 1.” This will initiate the download of a compressed (pdf) archive that contains the file.