Ultrastructure of a cryopreserved human sperm. The cryoprotectant used was glycerol/egg yolk. Ice was nucleated within the straw at -7°C. The sample was then cooled at 10°C per minute to -100°C and then transferred to liquid nitrogen. A cross fracture of the straw followed by deep etching removes ice and reveals a sperm embedded in a narrow zone of freeze concentrated material (non-etched material) with its tail and head extending into voids previously occupied by ice.
