68 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



of two mating types of a strain of Paramecium caudatum by Vivier 

 and Andre (1961). In addition to the usual dense, granular 

 chromatin and nucleoli, they illustrated bundles of fibrils coursing 

 randomly through the nucleoplasm. The fibrils were dense, about 

 25 mju, in diameter, and occasionally showed local zones of 

 hexagonal packing. Larger bundles were detectable with light 

 optics, and cytochemical tests showed that they contained neither 

 DNA nor RNA. They were negative to Sudan and periodic-acid 

 SchifF stains, but strongly positive to several protein tests. They 

 were observed over a period of several years in healthy, sexually 

 potent cultures, but possibly were more abundant in old cultures 

 than in young ones. Thus there was no evidence that they 

 accompanied any pathologic condition, and their significance is 

 a mystery. 



An extraordinary instance of highly organized structure in the 

 DNA-containing material of the ciliate macronucleus was 

 encountered by Rudzinska and Porter (1955) in the suctorian 

 ciliate, Tokophrya infusionum. Vegetative reproduction in these 

 suctoria is accomplished by endogenous budding, and the parent 

 cell maintains its identity through its reproductive period, then 

 ages and dies — a condition of cellular mortality not common 

 elsewhere among the protozoa. The macronucleus divides very 

 unequally during reproduction, the greater part of it being retained 

 by the parent. 



In an adult cell the macronucleus contains many small (0-5 /x), 

 Feulgen-positive bodies, and in electron micrographs these appear 

 as very dense, discrete spherules, composed of a compact filamen- 

 tous meshwork like the chromatin bodies of many other inter- 

 phase cells. In older cells, certain macronuclear granules appear 

 hollow by light microscopy, and additional, irregular, wispy, 

 Feulgen-positive bodies are seen. In electron micrographs the 

 hollow granules are seen to be composed of material with the 

 same density as before but showing a regular crystal-like order 

 (Fig. 28, PL VII). The pictures suggest a close hexagonal packing 

 of long, fine cylinders. The wispy material is composed of small 

 clusters or strands of the same organized structure. Older cells of 

 Tokophrya commonly undergo hemixis, a repeated division of the 

 macronucleus unaccompanied by cell division, and Rudzinska and 

 Porter speculate on the possibility that the appearance of the 



