128 PRACTICAL PAKASITOLOGY 



The eggs of Paramphistomum cervi (= Ampldstomum conicum], 

 which are of such frequent occurrence in the paunch of the ox, are 

 also easily hatched. The miracidia, which are exceedingly active, 

 develop in fresh-water snails of the family Physa. 1 



Much interesting material for experiment is suggested by the 

 current works on Helminthology. The student is offered a wide field 

 for investigation for, although a large number of Helminthes are 

 known to us, the complete developmental cycle has been traced out 

 in the case of but very few. 



CHAPTEK V. 



EXAMINATION OF HELMINTHES AND OF THEIR DEVELOPMENTAL 



STAGES. 2 



(1) TREMATODES. 



THE majority of the Trematodes observed in man are extra- 

 European in their occurrence, and but rarely available for purposes 

 of experiment. Generally speaking, the European varieties are 

 parasitic in man occasionally only, their normal hosts being the 

 domestic mammals, and this applies to many extra-European varieties. 

 Thus, Fasciola hepatica and Dicrocoelium lanceatum are normally 

 parasitic in the sheep ; Opisthorchis felineus in the cat. All three 

 species inhabit the gall-ducts of their host, but they vary in the 

 frequency of their occurrence. The commonest is undoubtedly the 

 liver-fluke (F. hepatica}, which is practically always obtainable 

 in Central Europe from the larger abattoirs. The lancet-fluke 

 (D. lanceatum) is also to be obtained from slaughter-houses, though 

 it is of somewhat less frequent occurrence than F. hepatica. 

 0. felineus, the fluke of the cat, is confined in Germany almost 

 exclusively to West and East Prussia. It occurs in other hosts 

 besides the cat in France, Holland, Scandinavia, Kussia, Hungary, 

 Italy, Siberia and Japan. 



The three European varieties are not equally valuable as subjects 

 for experiment. The liver-fluke, though readily obtainable, is of 

 but slight transparency and has considerable complexity of structure, 

 these characteristics rendering it a somewhat difficult subject for the 

 beginner. The lancet-fluke and the fluke of the cat are, when obtain- 

 able, better subjects for a first experiment. On account of their trans- 



1 A. Looss, " Mem. de 1'Inst. egypt.," vol. iii, 1896. 



2 Before making practical use of the information contained in the following 

 chapters, the student is advised to study the subject in M. Braun's " Animal 

 Parasites of Man." For Cestodes and Trematodes, Bronn's " Klass. u. Ord. d. 

 Tierreichs " should be consulted. 



