B y S. R. G R A V ES1, P. A. R A W L IN SO N 2, S. A. K E N N E L L Y -M E R R IT 3, D. A. M cL a r e n 4, K. J. H A R V EY 3 a n d I. W. B. T H O R N T O N 2 1 Department of M i c r o b i o l o g y , La Trobe UB undoor a, Victoria 3083, Australia 2 Department of Z o o l o g y , La Trobe Univers , Victoria 3083, Australia 3 Department of M i c r o b i o l o g y , Royal Melbourne , Victoria 3052...