PREFACE. 



SUTTON, Esq., F.RC.S., who has kindly permitted us to use his modification. 

 Except these and some others, whose source is acknowledged in the letterpress, 

 all the illustrations are taken from actual specimens, preparations, or dissections. 



The Drawings of Microscopic Specimens were first made to scale by means 

 of the camera, and then reduced. The sizes are given by a fraction. Thus 3 f 

 means that the Drawing was made under a power of three hundred diameters, 

 and then reduced to one-fifth of the size. " x 1 " signifies the natural size of the 

 object. 



Dr. H. ALEXIS THOMSON supplied us with several specimens of Animal 

 Parasites, and Dr. CARRINGTON PURVIS has given us much assistance in methods 

 of Preparing and Staining. Dr. LESLIE MACKENZIE gave us much valuable help 

 while the book was passing through the press. 



W. EAMSAY SMITH. 

 J. STEWAET NORWELL. 



EDINBURGH, April 1889. 



