The fixed tissue was washed in 10 mM citric acid–sodium citrate buffer (pH4.8) for 15 min prior to digestion in an enzyme mixture of 1%cellulase Onozuka R-10 (Kinki Yakult MFG CO., Japan), 1% cellulase from Aspergillus niger (0.32 U/mg, Serva), 20% pectolyase(0.70 U/mg, Serva) for 50 min at 37◦C.