6 



GUIDE TO THE STUDY 



should be especially sought at present, by mounting a little of 

 the black content of the rectum in salt solution. An excess of 

 water should be avoided. In order to get the best results the 

 mount should be sufficiently transparent to read ordinary print 

 through it. 



Opalina is a ciliated protozoan so large as to be visible to the 

 naked eye as a white dot. It is greatly flattened, covered 

 by minute cilia which give the surface distinct oblique striations. 



Fig. 2. — Recognition sketches of genera of common protozoal parasites of 

 frogs; except as noted, all from the intestine. 1-7, drawn to the same scale; 

 8-10 to one-third. 1, Endamoeba; la, Endamoeba cyst; 2, Trichomonas; 3, Tricho- 

 mastix; 4, 4a, Trypanosoma from blood; 5, Lankestrella in nucleated red cell; 

 6, Eimeria cyst containing four spores; 7, Lcptotheca spore from kidney; 8, 

 Opalina; 9, Nyctotherus; 10, Balantidium. {Adapted from various authors.) 



Numerous species have been described for frogs and other 

 batrachians. 



Balantidium entozoon is of especial interest because of its 

 close relationship to Balantidium coli, which is a serious parasite 

 of man. It is larger than the free-living Paramecium studied 

 in courses in general zoology and has a terminal gullet, lined by 

 cilia much coarser than those of the rest of the body. 



Nyctotherus cordiformis is similar to Balantidium entozoon but 

 is readily distinguishable by the presence of a gullet running 

 obliquely across the body rather than a terminal gullet as in the 

 latter species. 



