Cellular turnover in haemolymphatic tissues was assessed by counting proliferating and apoptotic cells. Proliferating cells were identified by their expression of the proliferating cell nuclear antigen (PCNA; [38] [39] [40] ), while apoptotic cells were demonstrated in situ by the TUNEL method ( [39, 41] ) using a commercially available kit according to the manufacturer's instructions (ApopTag TM In Situ Apoptosis Detection Kit; Chemicon, California, USA).