CHAPTER LXXIir. 



PAEASITIC DISEASES. 



REMARKS ON" CLASSIFICATION— NEMATODA— TREMA- 

 TODA— CESTODA— ACANTHOCEPHALA— DIPTERA— 

 TRACHEARIA— TABLES OF ENTOZOA. 



CLASSIFICATION OF PARASITES. 



Paeasites are distinguisliecl as Endoparasites when living in 

 the interior of their hosts, and as Ectoparasites when external. 

 "With the Ectoparasites we have at present nothing to do, but 

 will confine our attention entirely to the Endoparasites. Among 

 the most important endoparasitic animals or Entozoa are those 

 spoken of collectively as " worms," including not only round- 

 worms resembling the earth-worms {Lumhricus terrestris), and 

 hence popularly spoken of as Lumlricoids, but also worms 

 resembling a band or a tape (tape-worms), or a leaf (flukes), 

 as well as the thorny-headed worms {Echinorhynchus). The 

 round-worms and thorn-headed worms form together the class 

 Nematlielmintlics, while the flukes and the tape-worms constitute 

 the class Platyhelmintlies. These two classes form the parasitic 

 division of Cuvier's sub-kingdom Vermes. 



These classes are further broken up into natural orders ; thus 

 the class Nematlielmintlics includes the two orders Nematoda 

 and Acanthocepliala, and the elass FlatT/lielminthes the two orders 

 Trematoda or flukes, and Ccstoda or tape- worms. 



These natural orders are further subdivided into families, 

 genera, and species. Then, again, it must not be forgotten that 

 there are other kinds of internal parasites, commonly designated 

 " bots." These creatures are not usually classed with the entozoa, 

 or helminths proper, because they are merely the larval stages 



