80 NEMATHELMINTHES 



back from the anterior end. It can be seen only in favorable 



specimens. 



3. Open a well preserved or fresh specimen along the dor- 

 sal line and notice the definite cavity, and the straight ali- 

 mentary canal. If the specimen is a female, find the Y- 

 shaped genital organs, the free, ovarian ends of which are 

 slender and somewhat tangled. The position of the external 

 genital opening has already been noted. In the male there 

 is a single, tangled, threadlike testis, which joins the enlarged 

 seminal vesicle that extends to the cloaca. The nervous sys- 

 tem consists of a circumesophageal 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. 



Montgomery: The Adult Organization of Paragordius varius. Zool. 

 Jahrb., 18, 1903. 



TRICHINELLA 



Encysted specimens may occasionally be found by exam- 

 ining 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 trichinellae between 

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

 animal 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 trich- 

 inellae are abundant see if you can find more than one in 

 a cyst. 



