ACKNOWLEDGEMENTS 



Professor A. Graham, Professor G. P. Wells and Dr. R. B. Clark 

 have read various parts of the text and I am particularly grateful 

 to them for pointing out some of the mistakes resulting from my 

 ignorance of certain fields of physiology. Naturally they have no 

 responsibility for the errors that remain. I also wish to thank 

 my wife for her assistance in proof reading and Mrs. G. I. Smillie 

 for patiently typing and re-typing the script. 



Professor Knight- Jones wishes to acknowledge the help given 

 towards the appendix on marine leeches by Dr. N. Tebble of the 

 British Museum (Nat. Hist.) and by Dr. P. H. D. H. de Silva 

 of the National Museum, Colombo. 



