158 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



anterior end of the rostrum the parabasal fibrils appear to insert 

 on a pair of flat, stratified half-discs that are partly embedded in 

 a hemisphere of dense granular material (Fig. 65, PI. XVII). 

 Extending posteriad from this hemispherical complex, a rod of 

 similar dense material occupies the center of the rostral tube for 

 a short distance. According to Cleveland's (1960) light-micro- 

 scope studies, the hemispherical complex represents the anterior 

 ends of the two centrioles and the rod the posterior extension of 

 one of them ; at division the second also elongates and the mitotic 

 apparatus will be formed between the two posterior ends. Some 

 evidence of oriented lamellar structure is suggested in the central 

 rod in the micrographs of Pitelka and Schooley, but observations 

 of this critical area were too few to be conclusive. Grimstone 

 (1961), however, reports from unpublished studies by himself and 

 Gibbons the finding of a fibrillar centriole embedded in the 

 hemispherical complex. In the related trichonymphid flagellate 

 Barbulanjmpha, currently under study by J. Cook (personal com- 

 munication), neat rows of kinetosomes diverge from a filamentous 

 mass that represents part of the centriolar complex. Associated 

 with it (Fig. 64, PL XVII) are two kinetosomes that are markedly 

 out of alignment with the others. The posterior end of the 

 centriolar complex in the same species, sectioned during mitosis, 

 is a homogeneously dense, round body from which radiate the 

 tubular spindle fibrils (Fig. 66, PI. XVII). 



Kinetosomes of the rostral flagella in Trichonympha stand in 

 intimate contact with the outer surface of the rostral tube; 

 posterior to the circular fissure they stand free in the ectoplasm. 

 The parabasal fibrils twist about in the near vicinity of postrostral 

 kinetosomes, but there are fewer fibrils than postrostral rows of 

 flagella, and in any event the parabasal fibrils leave the rows of 

 kinetosomes when they curve medially to meet the parabasal 

 bodies. Kinetosomes, particularly on the rostrum, are extremely 

 long — up to 4 or 5 /x. Their nine component fibrils continue as 

 the peripheral fibrils of the flagella, which emerge from the 

 cytoplasm at the bases of deep longitudinal grooves. 



Considerably more detail concerning some aspects of these 

 flagellar structures is provided by the beautiful micrographs of 

 Gibbons and Grimstone (1960) The structure and orientation of 

 the flagellar and kinetosomal fibrils have been described in 



