PROTOZOA AS CELLS 67 



reorganization band. High-magnification pictures show that the 

 dense bodies are composed of very fine (about 8 m^) convoluted 

 filaments in compact masses. The reticulum of the reorganization 

 band is likewise composed of interlacing, possibly spiraled fine 

 filaments. Distal to the reorganization band, dense bodies 

 reappear, showing a graded increase in size over a space of less 

 than a micron. These do not differ appreciably from the pre- 

 existing granules. Thus the reorganization appears to be a process 

 of dispersion and reaggregation of a finely filamentous material 

 making up the DNA-containing macronuclear granules. That the 

 same phenomena characterize reorganization in E. patella is 

 demonstrated by the observations of Roth (1957). 



Gall's autoradiographic and photometric observations show 

 that DNA synthesis (measured as incorporation of tritiated 

 thymidine) occurs in a zone at the distal or posterior end of the 

 reorganization band, and that the total quantity of DNA in the 

 macronucleus is doubled by the time the bands meet. A basic 

 protein, presumably a histone, increases in a similar manner, 

 although precise quantitative data are not available. Gall's 

 evidence thus suggests "that the micronucleus contains a number 

 of DNA-histone 'units', presumably chromosomes, each of which 

 duplicates once and only once" (p. 295) in each interfission period. 

 To the general observer, the most interesting fact emerging from 

 a comparison of the papers by the electron microscopists and by 

 Gall may be that the chromosomal material is duplicated only in 

 a disaggregated state. 



Normal amitotic division of the macronucleus in Stylonychia 

 (Roth, 1960b) and Tetrahymena (Roth and Minick, 1961) is 

 accompanied by a coarse aggregation of granular elements and by 

 the appearance of fine (30 m/x) fibrils in the constriction zone. 



A unique nuclear structure has been reported by de Puytorac 

 (1959b) in the macronucleus of the astome ciliate Haptophrya 

 plethodonis. Here a dense chromatin network encloses many round, 

 vesicular nucleoli, each surrounded by a weakly-staining aureole. 

 In the electron microscope the latter is seen to contain concentri- 

 cally arranged, discontinuous lamellae, suggesting (but high- 

 resolution studies are needed) an intranuclear membrane system 

 not found elsewhere. 



Another curious nuclear inclusion was found in the macronuclei 



