PROTOZOA AS CELLS 63 



with nucleoli. At the same time, helices are reappearing, also 

 located peripherally, close to the nucleolar material. 



According to the account of these authors, the helices disappear 

 as mitotic chromatin appears, and vice versa. No evidence was 

 found to suggest that the helices were contributing through the 

 compaction of their substance or in any other direct way to the 

 formation of the early chromatin network. The visible morpho- 

 logy of the helices is so different from anything observed in any 

 other cell that the only clues to their significance are those 

 provided by wishful thinking. 



A very different and equally intriguing appearance is presented 

 by the giant chromosomes of some dinoflagellates. These persist 

 throughout interphase as long, coiled organelles attached to the 

 nuclear membrane by their chromomeres. Grasse and Dragesco 

 (1957) have examined species of Gymnodinium, Amphidinium, 

 Polykrikos, and a symbiotic zooxanthella from a sea anemone, and 

 Grell and Wohlfarth-Bottermann (1 957) have pictured Amphidinium 

 elegans. In all of these species, interphase chromosomes in thin 

 sections (Fig. 25, PI. VI) are seen to contain many filaments, each 

 3 to 8 m/x (Grell and Wohlfarth-Bottermann) or 13 to 14m/x 

 (Grasse and Dragesco) in diameter, coiled together in a helical 

 bundle, the coils being separated by a relatively coarsely granular 

 material. The French authors believed that the bundle represents 

 the chromonema and the individual filaments nucleoprotein 

 complexes. The coiling of the bundle is much grosser than that 

 of the filaments in the Amoeba nucleus, but the individual filaments 

 may be roughly of the same order of thickness. Grasse and 

 Dragesco reported occasional observations of the zooxanthella 

 chromosomes suggesting a finer coiling of filaments within the 

 maj or helical bundle. They believed that the granular nature of the 

 inter-fibrillar material probably was the result of coagulation 

 during fixation of a matrix substance. 



The macronuclei of ciliate protozoa generally appear by light 

 microscopy to be compact, as compared with the vesicular nuclei 

 of other groups. In electron micrographs a porous, double 

 nuclear envelope is seen to enclose a fine fibro-granular reticulum 

 set with randomly distributed, dense, fibrous or granular bodies 

 of irregular shape. These in a ciliate such as Paramecium (Fig. 27, 

 PL VII) (Tsujita, Watanabe, and Tsuda, 1957; Ehret and Powers, 



