PARASITIC ROUNDWORMS rji 



2 (3) Free-living in moist earth or water. Many embryonic and lar\'al 



stages of parasitic nematodes. 



Not distinguishable from free-living nematodes except by exact data cotK erninc sneiific 

 forms which are available only in a few cases. Such are the larvae of the human h(.<.kif.,rms 

 {Ancylostoma duodenale or Necator amertcanus), of Strongyloidcs stcrcoraiis known to Ik- nrcsi-nt 

 generally in infected areas. They depend for their development uixjn the opixjrtunilv of 

 entering a new human host. ' 



3 (2) Encysted in the viscera or flesh of various fishes. 



Agamonema capsular ia ( Rudolph i) 1802. 



The name covers what is probably a wide variety of different species from difTert-nt source* 

 Thus worms under this name are listed from migratory fishes, and these arc very likely to 

 represent encysted larvae of marine adults; and also from fresh-water fishes in which case 

 they are doubtless of fresh-water origin. The descriptions of these forms arc brief. Rcneral 

 and inadequate to differentiate larval forms of different genera. 



Among the other species recorded from North America are: 



Agamonema papilligerum, a single specimen of which was found by Leidy in Philadelphia, 

 in the body cavity of a pike. Later regarded by him as young FUaria solilaria. 



Agamonema piscium from the white fish, listed by Stiles and Hassall in the collection of the 

 Army Medical Museum. 



Such forms may be found in other hosts than fishes like the embryos recorded by Ix-idy as: 



Nematoideum integumenti lumbriculi limosi, encysted in the skin of a mud-inhabiting annelid. 



4 (i) Mature. Sexual organs developed; worms active, not encysted. . . 5 



Most adults are easily recognized as the eggs can be seen in the female and the sperm ma.s8 

 in the male. The open sexual pore in the female and the spicules in the male when exsertcd 

 aid in reaching a diagnosis. 



5 (6) Small transparent nematodes; in general appearance identical with 



free-living forms. Few eggs in uterus. 



Not a very satisfactory means of separating this group from certain species in the subse- 

 quent divisions which approach rather closely to the brief description of the key line above. 

 In case of doubt regarding a specimen the student should try also the latter alternative, 6 (5) 

 of the key. 



These forms are all minute (less than S to 6 mm. long). Furthermore they are simple in 

 structure and not easy to differentiate from free-living species. They possess a double es<iph- 

 ageal bulb and ventral glands often in lieu of lateral excretory canals. The male has two 

 similar spicules and in some cases a bursa. The female sexual pore is found in the posterior 

 half of the body and the uterus contains only a few thin-shelled eggs. 



One family, the Anguillulidae, includes the vinegar eel, the paste eel, various plant para- 

 sites of some economic importance, and many free-living forms. These do not show any alter- 

 nation of generations in the life history. 



Only group containing animal parasites. 



Family Angiostomid.ak iiraun 1S05. 



Characterized by heterogony. Otherwise very much hke the .\nguillulidae. and united 

 to them by many authors. Parasitic generation contains no males. 



Only genus recorded for North America. . Angiostomd Dujanlin 1845. 



Representative species in North America. 



Angiostoma nigrovcnositm ((ioczc) iSoo. 



In Biifo lentiginosiis; lung. District of Columbia. Listed by Stiles and Hassall under the 

 name Rhahdonema nigrovenosum as in the Bureau of .\nimal Industry C»»llection. 



6 (5) Nematodes larger than free-living species; almost always distinctly 



less transparent and often even oi)aque. I'tcrus contains 



many eggs ^ 



The unsatisfactory character of the key at this point has already been noted. The n«na- 

 todes which follow are usually well differentiated parasites, recognizable by one or another 

 typical structure not present in the previous group. They are, however, distinguishable irora 

 the latter only in general aspect and the key is open to doubt in a few cases. 



