ZOOFLAGELLATES 149 



them a very dense, homogeneous body identified as the centro- 

 some. The anterior tip of the axostyle, as in Tritrichomonas, curves 

 over the top of the kinetosome cluster, but does not in this picture 

 make contact with the centrosome. The axostyle is cut tangen- 

 tially and resembles the wall of the Tritrichomonas axostyle. A 

 striated fiber passes from the centrosome posteriad to the parabasal 

 body. 



A detailed and beautifully illustrated study of Pjrsonympha 

 vertens was published in 1956 by Grasse. This termite-inhabiting 

 flagellate is representative of a group whose affinities with the 

 trichomonad line are not clear. As seen in the light microscope, 

 the cell has the shape of an elongate pear, with four or eight 

 recurrent flagella inserting on a centrosome at the anterior end 

 and spiralling about the body surface to become free beyond its 

 posterior pole. From the centrosome also arise a long, slightly 

 flexuous axostyle and a shorter paraxostyle. At some periods in 

 the life cycle an organelle of attachment extends from the cell's 

 anterior tip into the tissues of the host gut. 



Grasse's electron-microscope studies show that the flagella 

 rest in well-marked shallow grooves in the cell surface (Fig. 59, 

 PI. XVI), from which they may occasionally be dislodged by 

 mechanical disturbance. The apposed membranes of cell and 

 flagellum are parallel and separated by a fairly constant gap. 

 Laterally, the flagellar membrane is expanded and convoluted 

 and often appears to engage like the teeth of a gear with crenellated 

 ridges on the cell surface bordering the groove. The flagellum 

 itself is of peculiar structure. The two central fibrils sometimes — 

 but not always — seem to be accompanied by one or two supple- 

 mentary ones. Besides these and the usual nine peripheral fibrils 

 there are from two to five additional linear structures. These are 

 dense and triangular in cross section, with the apex of each triangle 

 in contact with one of the peripheral fibrils of the flagellar axis 

 on the side facing away from the cell. The dense material may 

 appear homogeneous but more commonly encloses up to five 

 circular profiles resembling single flagellar fibrils. Distinct but 

 much smaller densities often appear on the medial side of the 

 axial fibril bundle. 



In spite of the fact that they adhere continuously to the cell 

 surface, the flagella of Pjrsonympha are motile; according to 



