Fig. 9. Mean number of BrdU-ir cells (per 100 µm lamella length) plotted against mean plasma T₄ levels for each sampling date. (A,B) Single and clustered BrdU-ir cells considered together. The data indicate a significant positive correlation in the basal cell layer (A) but not in the mid-apical cell layer (B), suggesting that T₄-induced proliferation is restricted to the basal cell layer. (C,D) Single BrdU-ir cells only. The data show a significant positive correlation in the basal cell layer (C) but not in the mid-apical cell layer (D).