NEMATHELMINTHES. 



Body elongated, cylindrical, and not segmented. They 

 have a very general distribution and a great diversity of forms. 

 Many are parasitic. Anus usually present. Coelom not filled 

 with parenchyma. The classes may not be genetically related. 



Class 1. Nematoda. 



Many are internal parasites, but others are found 

 in fresh and salt water and in damp earth. Body 

 pointed at both ends. Mouth terminal, anus ven- 

 tral. (Ascaris, Trichinella, Gordius.) 

 Class 2. Acanthocephala. 



Formidable intestinal parasites. Proboscis bearing 

 hooks. No alimentary canal. Macracanthorhyn- 

 chus (Echinorhynchus) . 

 Class 3. Chsetognatha. 



Marine, and all but one species pelagic. With caudal 

 and lateral fins and bristle-like jaws. (Sagitta.) 



ASCARIS. 



Animals belonging to this genus are common in the intestine 

 of the horse and pig, and are not uncommon in man. Examine 

 specimens and see if they have any organs that would aid them in 

 clinging to the intestinal wall. How can they retain their positions ? 



1. Can you determine which is anterior and which is posterior? 

 Is there any indication of segmentation? Can the ventral 

 side be distinguished from the dorsal? 



2. Find the mouth and see that it is bounded by three Hps. 

 Notice how these are placed and find the papillae on the ventral 

 ones. Find the anus and note its position. This serves also as 

 a reproductive aperture for the male. In the female the repro- 

 ductive aperture is situated about one-third back from the 

 anterior end. It can be seen only in favorable specimens. 



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