ROOT STRUCTURES 67 



(PI. IV and Va), found in the positions occupied by the neuromotor 

 fibrils investigated by Yocom (1918), Taylor (1920) and others. 

 These fibril bundles interconnect cirri and membranelles, and 

 Roth found a mass of intertwining fibrils at a point where fibril 

 bundles from cirri and membranelles converge; this may be the 

 *' motorium " of some light microscopists. The pellicle covering 

 the body surface is lined by subpellicular fibrils, again tubular and 

 about 220 A in diameter, running in two directions at right angles 

 and at slightly diflferent levels. Rootlet fibrils from the cirri also 

 connect with these subpellicular fibrils. 



Opalina is a protozoon with similarities to both ciliates and 

 flagellates, and, although it was formerly classified with the 

 ciliates, Grasse (1952) and Corliss (1955) have advocated that it 

 should be grouped with the flagellates. The cilia, or flagella, of 

 the body surface of Opalina are found in longitudinal rows, within 

 which they may be connected by structures described by Pitelka 

 (1956) and by Noirot-Timothee (1959). Some 7 or 8 short fibrils 

 about 150 A in diameter arise in each of two rows from each basal 

 body and follow a slightly curved course towards the next basal 

 body, running slightly to one side of the mid-line through the 

 basal bodies of the row. Fibrils of one row join to form pairs with 

 fibrils of the other row, and terminate near or possibly at the next 

 basal body (PL XIIIc). If the spiral twist of the triplets of fibrils 

 in the basal body of Opalina cilia shown in a micrograph (PL III, 

 Fig. 2) in the paper by Noirot-Timothee follows the pattern 

 generally found (Gibbons, 1961a), then the fibrils run forward on 

 the left, or backward on the right of the ciliary row. Also, if 

 Pitelka's finding that the fibrils run forward is correct, then the 

 fibrils pass towards the left of the ciliary row and not to the right 

 as do the kinetodesmal fibrils of ciliates. Fibrils which run 

 backwards and to the right are known in ciliates like Colpidium 

 and in the " kinetodesmata " of Stentor, 



Metazoan Cilia 



Long root structures may extend for a considerable part of the 

 length of metazoan ciliated cells, for the roots are seldom limited 

 to the surface layer as they are in many protozoa. The roots are 

 nearly always of the striated type in examples so far examined, and 

 this applies to both the specialized sensory cilia and normal 



