GENUS: GIAEDIA 695 



them; a pair of posterior flagella, the axonemes of which originate in the 

 anterior median blepharoplasts; and a pair of central flagella having 

 axonemes arising from the central blepharoplasts. The last pair of 

 flagella are thicker than the others, and usnally lie parallel to one another 

 on the surface of the body. As in the case of the axonemes of Hexamita, 

 those of the posterior flagella of Giardia are often regarded as axostyles, 

 but they cannot be homologized with the true axostyle of a TricJwynonas. 

 They undoubtedly represent the intracytoplasmic portions of the axial 

 filaments of the flagella, and are thus true axonemes. Simon (1922) 

 figures them as broad anteriorly at their attachment to the blepharoplasts 

 and tapering to a point posteriorly. Actually, they are of uniform 

 thickness throughout. Very frequently there occur two deeply-staining 

 curved or rounded bodies, which lie side by side just posterior to the 

 sucking disc and dorsal to the axonemes of the posterior flagella. They 

 are of largest size in the fully-grown individuals. These bodies have been 

 homologized by Kofoid and Christiansen (1915, 1915a, 19156) with the 

 parabasals of other flagellates, but there is little real evidence in support 

 of this view. The position of the blepharoplasts, as described above, 

 seems to the writer to be the true arrangement. Other observers have 

 considered that the axonemes of the eight flagella are all traceable to an 

 anterior group of four blepharoplasts, while Kofoid and Christiansen 

 (1915) in the case of G. muris and Kofoid and Swezy (1922) in the case 

 of G. intestinalis conclude that they all terminate in two, and suppose 

 that the presence of four in this region indicates the first stage in a division 

 process, each blepharoplast having divided to give rise to two. This 

 view is supported by Simon (1922) and Hegner (1922, 1922a). From the 

 appearances seen in G. intestinalis of man and G. muris of mice, as also 

 other forms, the writer believes that the undividing flagellate actually has 

 eight blepharoplasts, each of which gives origin to an axoneme of a 

 flagellum, as described above (Fig. 290). On a priori grounds alone, it is 

 highly probable that each flagellum has its own blepharoplast. This is 

 true of flagellates generally, and the members of the genus Giardia are 

 unlikely to be exceptions to the general rule. When the blepharoplasts 

 lie close together they often stain as a single body, so that the individual 

 blepharoplasts are difficult to detect. 



Several observers have described two fibres connecting the anterior 

 lateral blepharoplasts with granules on the anterior extremity of the 

 nuclear membrane. Bensen (1908) figures them in G. muris, while Kofoid 

 and Christiansen (1915, 1915a) describe in G. 'muris and G. microti a 

 continuation of these fibres to the karyosomes of the nuclei. They are 

 also figured by Kofoid and Swezy (1922) in G. intestinalis. The writer 

 has seen in G. intestinalis and other forms actual fibres connecting the 



