CILIATES 175 



dually from kinetosomes and extending to the right and anteriad 

 to form a loose bundle obeying the rule of desmodexy. Each 

 kinetodesmal fibril is broadly attached to the right anterior margin 

 of the base of its kinetosome, and extends past (but does not make 

 contact with) one or two kinetosomes anteriad before terminating. 

 In addition to these solid, striated kinetodesmal fibrils, three sets 

 of fine fibrils, all tubular in appearance and about 20 m/x in 

 diameter, occur consistently. One set is not directly associated 

 with the kinetosomes. It lies below the innermost pellicular 

 membrane to the right of each kinety, just above the kinetodesmal 

 bundle. Like the latter, it is composed of overlapping short units ; 

 these collectively form a continuous band, 8 to 14 fibrils wide, 

 that is apparent in isolated pellicle strips (Fig. 73, PI. XIX) and 

 evidently extends beyond the kineties to the extreme anterior pole 

 of the cell. A second set is a transverse band of about six fibrils 

 that arise at the left margin of each kinetosome (Fig. 74, PI. XX) 

 and passes up to the surface and laterally under the pellicle to 

 terminate in the region of the next longitudinal fibril band to the 

 left. The third set, the postciliary fibrils, arises as an oblique row 

 of seven or eight fibrils extending from the right posterior margin 

 of each kinetosome (Fig. 74, PI. XX). They spread out somewhat 

 as they pass up toward the pellicle and run posteriad to end in the 

 vicinity of the adjacent longitudinal fibril band to the right. 



Thus in these tetrahymenids each kinetosome of the somatic 

 infraciliature is the point of origin of three diverging fibrous 

 structures : the striated kinetodesmal fibril from its right anterior 

 margin, the transverse fibril band from its left lateral margin and 

 the postciliary fibrils from its right posterior margin. None of 

 these fibrils fuses, so far as can be detected, with fibrils from any 

 other kinetosome; there is no fibrous connection between kinetosomes, 

 except in the buccal region where tracts of fine filaments do 

 interconnect them. 



Each somatic cilium of the tetrahymenid arises from a boat- 

 shaped depression of the cell surface. The external pellicular 

 membrane lines this depression and extends to cover the cilia. 

 The rims of the adjacent pellicular alveoli, indented to permit 

 egress of the ciliary fibrils, become thickened and fuse to form a 

 continuous ring or short sleeve about the upper end of the kineto- 

 some. Just anterior to the cilium, the cell surface invaginates in a 



