INTRODUCTION o 



ourselves, the bodies of animals are to them. To attack, to 

 invade, to infest, is their legitimate prerogative. Their organi- 

 sation, habits, and economy are expressly fashioned to this end. 

 How remarkable and complex is their structure, and how pecu- 

 liar, diverse, and varied are their ways and wanderings, the 

 contents of this volume will, I trust, sufficiently explain. The 

 puerile horror which even some scientific persons affect to 

 display in regard to the subject is altogether out of place. To 

 the rightly balanced mind the study of these much abused 

 " worms " is just as attractive as any other section of zoology. 

 Helminthology opens up to our view many of the strangest 

 biological phenomena of which the human mind can take 

 cognisance ; whilst a profound and extended knowledge of the 

 subject, in all its bearings, is calculated to secure to the com- 

 munity a rich practical reward by enabling us to do effectual 

 battle with not a few of the many ills of life to which our flesh 

 is heir. 



Further on the general advantages to be derived from the 

 study of parasites I cannot here dilate, and it becomes the less 

 necessary that I should do so, since I have entered upon the 

 subject very fully elsewhere. The character of the present work, 

 moreover, imposes brevity. If the plan which I now propose 

 to follow should not be deemed altogether satisfactory from the 

 purely zoological standpoint, it will nevertheless have the 

 advantage of simplicity and novelty ; and knowing full well the 

 difficulties that must surround any attempt to give a perfect 

 classification of the entozoa, considered as a natural group, I feel 

 sure that my helminthological friends will credit me with 

 exercising a wise discretion in selecting the simplest available 

 method of arrangement. My plan, therefore, is to devote 

 separate sections of this work to the parasites of the different 

 classes of vertebrated animals, including man, treating of the 

 various species in regular succession. This arrangement is 

 merely one of convenience and has no reference whatever to 

 conceptions of zoological equivalency as variously interpreted 

 and maintained by authors and investigators. The parasitic 

 groups will be taken up in the following order, quite irrespective 

 of their relative importance, and also without any attempt to treat 

 each group with equal fulness. In the matter of recent literature 

 only will the present record and summary make any approach 

 toward completeness, my hope being to render this treatise 

 indispensable and trustworthy as a ready means of reference. 



