GENERAL REMARKS 231 



that name. One man may describe the creature found but 

 another may name it ; this latter person is the author. 



(2) The Rule of Priority. 



The first name given must be adopted by all unless rendered 

 invalid. Hence Trichina was found to have been applied to an 

 insect some 50 years before it was applied to the new worm and 

 consequently was changed to *' Trichinela." 

 Different spelling can be a different name. 



(3) The Rule of Homonyms. 



When two distinct genera and species of animals receive the 

 same name that name applied first must stand. 



(4) The Rule of Appropriateness . 



No name is allowed to be changed simply because it is inappro- 

 priate. An author cannot reject the name he has once given. 



THE GROUPING OF HELMINTHS. 



Helminths occurring in the human intestine belong to two distinct 

 groups of the animal kingdom, viz. : — 

 (i) Platyhelmia, (2) Namathelmia. 



Platyhelmia. 



These are flat and leaf-like. There is no body cavity. 



The mouth is at the anterior end, or near to it, and is on the ventral 

 surface. It is simple, forked or branched, but always blind. 



There is no hind gut or anus. 



The muscular fibres are angular, longitudinal, and circular. 

 • The excretory system is highly complicated and consists of a 

 branched set of tubules discharging at or near the postero-central 

 surface. 



The sexes are not separate with two exceptions, the important one 

 being the Bilharzia haematobium. 



There are two classes of Platvhelminths, Trematoda and Cestoda. 



Cestodes are really proliferating trematodes. The latter consist 

 of a single segment, the former of many. The latter have an alimen- 

 tary canal, the former none. 



For classification see next page. 



The species will be described according to their pathogenicity in 

 man under their respective headings. 



Nemathelmia. 



These are bilaterally symmetrically thread-like with a distinct 

 cavity between the body wall and the gut in which the genital organs 

 freely float. 



The alimentary canal, when present, is a straight tube from mouth 

 to anus, or it may be absent. 



