Embryonic day (E) 15 chicks or 2-year-old adult chickens were perfusion-fixed with 2% paraformaldehyde plus 2% glutaraldehyde in cacodylate buffer, pH 7.4. Ciliary ganglia were removed, transferred to fresh fixative, and incubated for 3 hr at room temperature. Adult ciliary ganglia were cut into 1 mm3 pieces. After being rinsed several times in 0.1 M sodium cacodylate buffer, pH 7.4, the tissue was treated for 30 min with 2% osmium tetroxide in 0.1 M sodium cacodylate and then counterstained with uranyl acetate. The ganglia were dehydrated in a series of ethanol solutions followed by two rinses in acetone, infiltrated with Durcupan ACM resin (Electron Microscopy Sciences, Fort Washington, PA), allowed to polymerize for 24 hr at 60° C, and then sectioned. For serial tomography a continuous series of 10 1-µm-thick sections was prepared to encompass a complete spine mat. For traditional thin section analysis 100-nm-thick sections were made.