vi PREFACE 
hundred terms when ill-health prevented his continuing the 
work, and it was handed over to the present authors. 
We have to acknowledge our indebtedness to Professor 
J. H. Ashworth of Edinburgh University, who has very kindly 
read over the manuscript and given us some suggestions for 
additions. 
je ae 2 
ZOOLOGY DEPARTMENT, 
UNIVERSITY OF BRISTOL. 
