17 



two lung parasites of slieep in tlie Old World that have not been found 

 here, viz : Strotujylus rufescens, Leuckart, and S. miiiutissimus, Megnin. 

 The former is said to occur iu Germany and France, but is so meagerly 

 described that it probably is not a distinct species, but a synonym of 

 Strongylus {PseudaliHs) ovis-^mlmonalis, Diesing. The latter occurs in 

 Algeria, is well described and figured, and seems to be a well estab- 

 lislied species. Strongylus ventricosuSj also a European species, has 

 not, to my knowledge, been described as a parasite of sheep heretofore. 



A further comparison of the above list with those of parasites of sheep 

 in other countries is re-assuring, because, first, native sheep have now 

 nearly all the parasites that they can acquire in this country; second, 

 that although nearly all the European species have been imported, Bis- 

 toma hepaticum, L., the liver-fluke, Tmiia .echinococcus, v. Siebold, and 

 T. coemirns, Kiich., are either very rare or else do not exist in this coun- 

 try. These three parasites have been the cause of great .loss among 

 sheep in other parts of the world. 



The comparatively long list of parasites furnished will seem to the Eu- 

 ropean to indicate that sheep in this country are more infected than 

 those in Europe; but iu this connection it should be remembered that 

 much time has been spent in hunting for several of these species, and 

 some of them are rare, inconspicuous, and do little damage. 



The following is a list of our most destructive ovine parasites: 



Oestrus ovis, L.; Psoroptes comtmmis, Fiirst.; Tamiajimbriata, Diesing; 

 T. expansa, Eud.; Strongylus contortus, Kud.; Dochmius cermms, Creplin; 

 Q^sophagostonia Columbianum, Curtice; Strongylus ovis-pulmonalis, Dies- 

 ing ; and S.filaria, Eud. There are nine species in all, a list which 

 compares favorably with that of the ovine parasites of any other coun- 

 try ; for all but two species, T. Jimbriata and 0. Golumbianum, are com- 

 mon to all countries, and these two are more than offset by the i)reva- 

 lence of more destructive parasites in the Old World. 



On the whole, the flockmasters of the United States may be congrat- 

 ulated on the good condition of their flocks and their comparative free- 

 dom from both external and internal parasites. 



PARASITISM. 



Definition. — The animal parasites of sheep are those which live in or 

 upon their living bodies and obtain nourishment from them. The term 

 " animal parasites " is used in order to distinctly separate this group 

 from ^he vegetable parasites which attack the living organs of sheep. 

 Both animal and vegetable parasites prey upon the flocks and cause 

 disease, but such are the differences between them, their effects and the 

 methods of investigating them, that an investigation of either forms a 

 large field of research. 



Parasites as defined above include a large number of animals so dif- 

 ferent from one another that parasitism is the only common character 

 23038 A P 3 



