1923] Hall: Binary Fission of Menoidium incurvum 465 



The Prophase 



Tsclienzoff (1916) describes the prophase as beginning in Euglena 

 viridis when the chromatic substance begins to form distinct granules, 

 which later become arranged in rows to form chromatic threads. He 

 notes the appearance of an increasing number of chromatic granules 

 which lie at the nuclear surface and appear to crop out into the 

 cytoplasm, producing wrinkles in the nuclear membrane. These 

 mysterious granules are believed either to break up and pass out into 

 the cytoplasm, or else to take part in the formation of chromosomes. 

 Later the chromosomes become arranged more or less radially around 

 the endosome ; with the elongation of this structure, the chromosomes 

 come to form a cylindrical ring parallel to its long axis. Dehorne 

 (1920), in a comparative study of the euglenoid and other protozoan 

 nuclei, comes to the conclusion that, as Dangeard (1902) believed, 

 the nucleus of Euglena contains in the prophase a continuous 

 chromatin thread; this 'spireme' is said to be composed of granules. 

 He bases his statement on the appearance of loops in the chromosomes 

 and the fact that he is unable to find free ends ; however, his figures 

 do not afford sufficient evidence to convince one of the accuracy of 

 such an interpretation. 



In Menoidium these early processes are similar to those described 

 by Tschenzotf, with the exception that no granules, such as he men- 

 tions, have been observed. In many cases structures resembling these 

 granules of Tschenzoff have been seen, but they can always be resolved 

 into optical cross-sections of chromatin threads. It is thus possible 

 that Tschenzoff has mistaken optical sections of chromatin threads for 

 actual granules ; such an explanation might account for most of these 

 structures shown in his figures. 



In connection witli the formation of chromosomes in the prophase. 

 Sands (1922) presents some rather startling conclusions drawn from 

 his work on Tradescantia virginica. He states that in the so-called 

 resting stage, the genes attract to themselves "from the protoplasm, 

 materials of a similar kind, thus molding next to the original gene 

 another structure of similar parts, identically arranged, which then 

 become bound together to form another gene, a replica of the first," 

 and that these genes ' ' after the genesis of their like, reassemble in such 

 a fashion that they form a continuous spireme thread. ' ' He also states 

 that the chromosomes are formed in the prophase by segmentation of 

 a continuous spireme, and that no longitudinal splitting of the chromo- 



