CHAPTER III. 

 PLATYHELMINTHS. 



THE Platyhelminths are worm-like bodies, flattened 

 dorso-ventrally, frequently hermaphrodite, and with an 

 anteriorly placed central nervous system. If there are 

 intestinal tubes they are blind, and as there is no rectum 

 are said to be aproctous. The excretory system consists 

 of ramified tubes. There is no body-cavity. Muscle- 

 fibres are non-striated. There are three main divisions 

 or classes : 



CLASS I, Tiirbellaria, are free-living platyhelminths 

 covered with a ciliated ectoderm. They are not parasitic. 



CLASS II, Trcmatoda or Flukes, are parasitic platy- 

 helminths. They are unsegmented and usually flattened 

 or leaf-shaped, but in some species the females are cylin- 

 drical. Most species are hermaphrodite. They possess 

 a mouth, opening into an expanded muscular ring or 

 sucker. There is a straight muscular oesophagus which 

 divides into two blind diverticula or caeca. There is 

 no anus. A second sucker, or acetabulum, in addition 

 to the oral sucker, is usually present and serves for 

 fixation. 



CLASS III, Cestoda (Tapeworms), are elongated flattened 

 and segmented platyhelminths. There is no alimentary 

 canal, and the organs for attachment are at the anterior 

 end of the worm. In each mature segment there are 

 complete male and female reproductive organs. These 

 are considered later. 



TREMATODA. 



The Trematoda parasitic in man are, as far as we 

 know, all digenetic, meaning that the life-cycle from egg 



