The sectioned lizard tails were fixed in 4% paraformaldehyde and 2% glutaraldehyde in 0.1M cacodylate buffer at pH 7.4 (23 , 32 (link)). The tails were fixed for 12 to 16 h at room temperature and then rinsed four times in cacodylate buffer, then postfixed and stained with 1% osmium tetroxide and 1.5% potassium ferricyanide in 0.1M cacodylate buffer for 1 h. Tissues were then washed four times in cacodylate, dehydrated in increasing concentrations of ethanol, rinsed twice in propylene oxide, infiltrated with increasing concentrations of Agar 100 resin in propylene oxide, and embedded in fresh resin. Ultra-thin (80 nm) cross-sections were cut with a diamond knife on a LKB 3 microtome. The cross-sections were then placed on carbon-formvar-coated copper grids and were poststained with uranyl acetate and lead citrate. TEM imaging on the ultra-thin biological tissues was performed using a Tecnai 12 TEM 100 kV (Phillips) equipped with MegaView II CCD camera. The TEM images were collected from three hatchling specimens and two adult specimens, which include hundreds of cells from hatchling to adult in total.