8 THE ROUNDWORMS OF DOMESTIC SWINE. 



Nothing is known in regard to the life cycle of these parasites, but their wide distri- 

 bution and frequency of occurrence suggest a simple life history without an interme- 

 diate host. The fact that the eggshells of both species are relatively thick would 

 seem to indicate that the embryos are not liberated until the shell is dissolved by the 

 gastric juice of the host. From the fact that the embryos are fairly well developed 

 before oviposition, it may be inferred that the eggs require but a short period of incu- 

 bation. 



Following the discussion of the two species is a key for use in the identification of 

 round worms parasitic in swine; also a list of these parasites classified according to their 

 zoological position. 



INTRODUCTION. 



Nematodes occurring in the stomach are commonly present among 

 swine in the United States. These have usually been considered by 

 veterinarians, pathologists, and others who have had occasion to 

 mention them as belonging to the species Spiroptera strongylina 

 Rudolphi, 1819, although some have expressed a doubt as to the cor- 

 rectness of the identification. In addition to the forms which have 

 been identified as Spiroptera strongylina, Hassall and Stiles (1892a) 

 have described a species named by them Strongylus rubidus, and 

 which has since been collected from domestic swine in Europe. 



Recently a zoological study of specimens of nematodes in the hel- 

 minthological collection of the Bureau of Animal Industry, collected 

 from the stomachs of hogs in various parts of the United States, was 

 undertaken by the present writer, largely as a result of reports from 

 inspectors relative to the prevalence of nematodes in the stomachs 

 of swine, Drs. J. J. Brougham and T. B. Pote, of the St. Louis station, 

 having been among the first in the Federal service to give attention to 

 the subject from the standpoint of meat inspection. As a result of this 

 study and of a comparison of these specimens with specimens of 

 Spiroptera strongylina received from Europe, the conclusion has been 

 reached that in several particulars the descriptions of Spiroptera 

 strongylina commonly given by European writers are in error, and 

 that the forms commonly identified as Spiroptera strongylina represent 

 two distinct species, one of them Spiroptera strongylina, the other cor- 

 responding to Physocephalus sexalatus (Molin, 1860) Diesing, 1861, 

 hitherto considered a rare parasite and until recently reported only 

 once for domestic swine. 



According to Stiles and Hassall (1905b), the genus Spiroptera is 

 preempted by the genus Acuaria Bremser, 1811, whose type is 

 anthuris. This species is also the type of Dispharagus Dujardin, 1845, 

 a genus based largely on certain nematodes of birds and not found in 

 mammals. According to this ruling, the genus Acuaria is confined to 

 certain parasites of birds and fishes characterized by a differentiation 

 in the structure of the esophagus. As Spiroptera strongylina does 

 not conform to the type of Acuaria or the characteristics of the genus, 

 a new genus to include these forms is necessary. This deficiency has 



