72 GUIDE TO THE STUDY 



rats, but the very closely related species commonly infesting rats 

 is Giardia muris. Other related species are found in rabbits, 

 guinea-pigs, and numerous other animals. The organisms are 

 the shape of a longitudinally cut half of a pear with a large 

 concavity, or sucking disk, at the anterior end. They move in 

 a characteristic manner, rotating on their long axis in a jerky 

 manner. The size and relative breadth vary with the species, 

 though considerable variations occur in the same species. A 

 striking peculiarity of representatives of the genus is the duplica- 

 tion of organelles. There are four pairs of posteriorly directed 

 flagella, two prominent nuclei, and two rodlike longitudinal 

 axostyles. Just posterior to the sucker is an obliquely placed, 

 deeply staining mass which represents a pair of more or less 

 fused parabasal bodies. 



The cysts are hyaline, oval bodies with a well-marked refractile 

 membrane and exhibit two or more nuclei and traces of the 

 fibrillar apparatus in the living condition. Specimens well 

 stained in iron hematoxylin show the basal portions of the 

 flagella and the axostyles in the younger cysts. There are 

 usually four nuclei in the older ones, and in some cases eight 

 and even more have been noted. Near the posterior part of the 

 cyst are paired, coarser, deeply staining fibrils whose significance 

 is still in dispute. 



References 



Becker, E. R., 1926. The flagellate fauna of the caecum of the striped 



ground squirrel, Citellus tridecemlineatus, with special reference to 



Chilomastix magna sp. nov. Biol. Bull., 51(5): 287-298. 

 Boeck, W. C, 1921. Chilomastix mesnili and a method for its culture. 



Jour. Exptl. Med., 33(2): 147-175. 

 Dobell, C. C, 1909. Researches on the intestinal protozoa of frogs and 



toads. Quart. Jour. Micro. Sci., 53 (2): 201-277, plates 2-5. 

 Hegner, R. W., 1923. Giardias from wild rats and mice and Giardia 



cavia sp. nov. from the guinea-pig. Am. Jour. Hyg., 3 (3): 345-349. 

 Kofoid, C. A., and Olive Swezy, 1915. Mitosis and multiple fission in 



trichomonad flagellates. Proc. Am. Acad. Arts Sci., 51 (6): 289-378, 



plates 1-8. 

 Kofoid, C. A., and Olive Swezy, 1922. Mitosis and fission in the active 



and encysted phases of Giardia enterica (Grassi) of man. Univ. Calif. 



Pub. Zoology, 20 (8): 199-234, plates 23-26. 

 Martin, C H., and Muriel Robertson, 1912. Further observations on 



the caecal parasites of fowls, with some reference to the rectal fauna of 



other vertebrates. Quart. Jour. Micro Sci., 57 (1): 53-82, plates 10-14. 



