Résumé : The authors regret that the legends of Figs. 8, 9 and 10 have been presented in a wrong sequence. For the caption of Fig. 8, see Fig.10 (Page 103). For the caption of Fig. 9, see Fig. 8 (Page 101). For the caption of Fig. 10, see Fig. 8 (Page 102). The authors would like to apologise for any inconvenience caused.