CILIATES 211 



In addition to the retrociliary fibers coursing every which way 

 through the anterior ectoplasm, tracts of filamentous material 

 that apparently derive from the innermost layer of the pellicle are 

 seen in electron micrographs of the region of the rectum and at 

 various sites in the anterior part of the body. A network of such 

 filaments spreads over the outer surface of the skeletal plates and 

 extends anteriad as a heavy tract to a sizable aggregate of inter- 

 laced filaments in the ectoplasm adjacent to the adoral ciliated 

 zone. Noirot-Timothee identifies this aggregate as the so-called 

 motorium of light microscopy. Some other bands of filamentous 

 material she concludes represent caudal, rectal, peri-esophageal, 

 and circumciliary fibrils seen in hematoxylin-stained light- 

 microscope preparations. Electron micrographs did not permit 

 recognition of a complex silverline system concentrated around 

 the ciliated zones. 



The skeletal plates of the ophryoscolecids consist of packed 

 prisms of homogeneous, low-density material, lacking limiting 

 membranes but often surrounded by aligned cisternae of granular 

 membranes. They are composed of a neutral polysaccharide, not 

 glycogen. Noirot-Timothee considers that they represent 

 nutritive reserves, perhaps secondarily providing mechanical 

 support. Other polysaccharide granules are commonly distributed 

 throughout the cytoplasm in well-fed organisms. 



Both Bretschneider and Noirot-Timothee note the occurrence, 

 on one side of the adoral zone of syncilia, of a single row or small 

 clump of cilia that are not aligned with the adoral band and that 

 in cross-section look quite different. Their diameter is greater 

 than usual owing to an expanded matrix zone between the axial 

 fibril bundle and the surface membrane, and the matrix is notably 

 less dense than that of ordinary cilia. Bretschneider suggests that 

 these may be specialized sensory organelles. 



A particularly intriguing question concerns the ontogeny of 

 the ciliated zones in the entodiniomorphs. The first evidence of 

 impending cell division is the appearance of an adoral zone anlage 

 within a vesicle in the ectoplasm of the presumptive posterior 

 daughter cell, far removed from the parent ciliature. Noirot- 

 Timothee shows electron micrographs of several of these vesicles, 

 which are lined by a unit membrane and contain rows of kineto- 

 somes along the inner wall. In later stages cilia emerge from the 



