ENTOZOA. 



CHAPTER I. 



HELMINTHA. 



Nature and extent of the subject — Leading terms employed — The Entozoa constitute 

 a peculiar fauna — Their distribution throughout time and space — Not yet found 

 in a fossil state — Classification of the Helminths— A new sub-class proposed — 

 The Turbellarians — Characters of the Planarid^ — Genera — The Nemertidee, or 

 ribbon worms — Their structure and habits — G-enera — Concluding argument in 

 favour of associating the Turbellarians with the Helminths in the manner here 

 proposed. 



Of late years no department of Natural History science has 

 attracted more attention than that of the study of internal 

 parasites, and it may also be affirmed that no separate branch of 

 biological inquiry has in recent times advanced more rapidly. 



The study of the internal parasites of man and animals is one 

 of boundless extent, and from the multiplicity and variety of crea- 

 tures thus found associated by one common habit of life, zoologists 

 have deemed it not only advantageous, but even absolutely 

 necessary to consider them collectively in the light, as it were, of 

 a separate science. To this science the appropriate title of 

 Helminthology {e\fMLv9e<i — X0709) has been given ; but the term Ento- 

 zoology (ei/ro? — ^coov — ^070?) is nearly equivalent, and may be 

 conveniently substituted when occasion offers. 



Helminthological science makes us acquainted with the forms, 

 habits, structure, development, distribution, and classification of a 

 multitude of evertebrated organisms which take up their abode, at 

 one or more periods of their lifetime, in the bodies of man and 



