Lenses bisected along the optical axes were immersion fixed in 2% (w/v) paraformaldehyde and 2% glutaraldehyde (v/v) in 0.1 M sodium cacodylate buffer pH 7.2 at RT for 24 hrs. Samples were then washed several times with distilled water and postfixed in 1% (v/v) aqueous osmium tetroxide at RT for 1 hr. Lens halves were dehydrated in an ascending ethanol series from 50–100 %. Once lens halves were in 100% ethanol, they were critical point dried in carbon dioxide in a Samdri-790B (Tousimis Research Corp., Rockville, MD). Critical point dried lens halves were secured on aluminum stubs with double sided tape. Mounted specimens were then sputter coated with gold and viewed on a Hitachi S-3500N scanning electron microscope (Tokyo, Japan) at 1–5 kV. This microscope is equipped with Hitachi's patented "Dual-Bias" which allows extremely high emission currents at acceleration voltages of 5 kV and lower.