TRICHINA. 47 



what tangled. The position of the external genital opening has 

 already been noted. In the male there is a single, tangled, thread- 

 like testis, which joins the enlarged seminal vesicle that extends 

 to the cloaca. The nervous system consists of a circum-esopha- 

 geal ring, six longitudinal nerves, the dorsal and ventral of 

 which are larger than the others, and anterior nerves. It is 

 not easily seen. 



A drawing is desirable. 



TRICHINA. 



Encysted specimens may frequently be found by examining 

 thin pieces of pig muscle obtained from the meat market. Pigs 

 fattened in small pens and fed on table waste, or in slaughter- 

 yards and fed on the offal of butchered animals, are much 

 more likely to be infected than others. Scavenger rats and 

 cats are frequently infected. 



1. Flatten a piece of muscle containing trichinae between 

 two slides in a little glycerin and notice the relation of the ani- 

 mal to the muscle fibers. Notice the cyst that surrounds it 

 and see if you can determine whether this was formed by the 

 host or the parasite. There are frequently fat cells at the ends 

 of the cyst. Just after the parasites are encysted, the cysts are 

 surrounded by capillaries that may be injected by injecting the 

 vessels of the host. These may be found only at a definite stage 

 after encystment. Why are they formed? Do they indicate 

 how the cysts were formed? If the trichina) are abundant see 

 if you can find more than one in a cyst. 



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 intestine 

 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. 



