ASCARIS, TRICHINELLA, METONCHOLAIMUS 81 



2. Notice the shape that is assumed by the parasite. Is 

 the coiling always the same? If your material is fresh, mount 

 some of the muscle between slides without glycerin, warm the 

 slide, and see if the encysted animals will move. 



3. Are the anterior and posterior ends alike? Is there any 

 indication of a mouth? The large cells that form the intes- 

 tine can frequently be seen. It should be borne in mind that 

 the encysted specimen is not fully adult and that the animal 

 grows after reaching the alimentary canal of the next host. 



Make a drawing of an encysted animal. 



Glazier: Report on Trichinae and Trichinosis. U. S. Treas. Dept. Doc. 

 No. 84, Marine Hospital, 1881. 



METONCHOLAIMUSi 



This species, Metoncholaimus pristiurus, is a free-living 

 nematode found in the mud in shallow salt water. It belongs 

 to a large marine group, the Oncholaiminae (type genus, 

 Oncholaimus, "tooth in the throat"). 



1. Make a preliminary examination of several specimens 

 in a Syracuse dish using a binocular dissecting microscope. 

 Observe the characteristic coiling and uncoiling movements. 

 Distinguish the blunt anterior end from the more pointed pos- 

 terior end. In some specimens large beadlike structures may 

 be seen near the middle of the body. These are eggs and 

 serve to identify the females. 



Select a female and place in a drop of fresh water for one 

 to two minutes until it is quiet and then mount immediately 

 in clear sea water. Flatten the animal slightly by removing 

 water from under the cover glass. 



2. The Digestive System. — Note that the posterior end 

 tapers rapidly and is slightly curved. The anterior end 

 tapers gradually. Along the sides of both are numerous sen- 

 sory setae. The mouth is at the truncated extremity of the 

 anterior end. Behind the mouth is the short pharynx with 



a The laboratory directions given above have been adapted from 

 directions originally furnished by the late Dr. N. A. Cobb. 



6 



