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 geneti- 

 cally 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 bear- 

 ing hooks. No alimentary canal. Macracantho- 

 rhynchus (Echinorhynchus) . 



Class 3. Chaetognatha. . 



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 intes- 

 tine 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 pos- 

 terior? 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 lips. 

 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 reproductive aperture is situated about one third 



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