FINE STRUCTURE 3I 



waves passing along it after patches of cilia were detached ", but 

 no one has confirmed this. That the oral lip is capable of indepen- 

 dent contraction Hke a sphincter suggests some means of developing 

 tension in the transverse direction. Whether actively or passively, 

 the membranelles of the entire band do come closer together 

 when the frontal field is contracted (Randall and Jackson). 



Each membranelle has an extension into the endoplasm. 

 Difficult to observe, the structure and function of these processes 

 have occasioned conflicting interpretations, but recent studies with 

 the electron microscope clarify the issues. Schuberg (1890, 1905) 

 described a triangular sheet or lamella from the base of each 

 membranelle, apparently bordered by two converging fibers and 

 narrowing inward to an apex which continued as an end fiber, 

 while the end fibers of all the membranelles were joined together 

 by a deep-lying basal fiber. Most workers agreed with this picture 

 (excepting Schroder, Neresheimer, and Dierks) and EM studies 

 are confirmatory. Neresheimer (1903) interpreted the lamellae as 

 overlapping plates which were not joined by a continuous fiber and 

 served for anchoring the membranelles. This view was expanded 

 by Dierks (1926a) who described the lamellse as anchoring 

 rectangles with a twist which accounted for the other appearances 

 including the basal fiber. In the light of the EM studies this view 

 will be discarded, and also it may be added that in shed 

 membranellar bands nothing like these plates is found, as would 

 be expected if they had sufficient strength to serve for anchoring. 



Faure-Fremiet and Rouiller (1955) made an EM study of 

 polymorphtis, niger and coeruleus. They find that each membranelle 

 is composed of two short, parallel rows of ciliary basal granules or 

 kinetosomes which are connected to each other laterally and give 

 off ciliary rootlets into the interior. Each bundle of rootlets com- 

 bines with that from neighbouring cilia to form the triangle 

 Schuberg described, which is now seen to be of a fibrous nature 

 throughout. Randall and Jackson confirmed this picture and added 

 new details (Fig. 5). The fibrils in the triangular bundle are fitted 

 together in an orderly stacking. These fibrils do not appear to be 

 striated, as is the case with some metazoan ciliary rootlets (Fawcett 

 and Porter, 1954). Continuing inward, the fibrils form a long 

 bundle, corresponding to Schuberg's end fiber, and these are in 

 turn joined together at their ends by a composite basal fiber. The 



