1919] KofoidSwczy: Trichoiiijmpha campanula 65 



strnctural units in its make-up, according to the nature of the cell in 

 which it occurs — even so diverse as the neuromotor sj^stem of a 

 flagellate and the sol phase of reversible cytoplasm. It is the organ- 

 ization rather than the state of the substance that is significant. 



Mitosis 



Evidences of the approach of division may be looked for in the 

 nucleus before any changes may be apparent in either the ectoplasmic 

 structures or the external form of the body. The changes that take 

 place in the nucleus relate to the formation of the chromosomes, and 

 are significant both from the standpoint of their later history and 

 of the question of the continuity of the chromosomes. Their develop- 

 ment will now be taki^n up in detail. 



Prophase: The structui-e of the vegetative nucleus shown in 

 figures 11 and 14 of plate 6, has already been described. The central 

 masses of chromatin seem to lie at the intersections of the linin 

 reticulum, in some cases (fig. 11) the individual masses being large 

 enough to completely fill the interstices also. In the early prophase 

 the outer alveoli disappear, leaving a clear space with a granular 

 region near the membrane (pi. 6, fig. 15). This granular material 

 later becomes diffused thi-ough the entire intranuclear spaces and 

 persists throughout mitosis. The chromatin moves out from the 

 rounded particles along the lines of the reticulum, sometimes before 

 the alveolar zone has disappeared (fig. l-l). This movement becomes 

 more evident with the change in the outer region of the nucleus, and 

 a slight expansion takes place, with the chromatin filling a larger area 

 than is usual in the vegetative stage. 



The outpushing of chromatin from the central masses is not equal 

 in all directions. This may be due to a lack of continuity in the linin 

 reticulum or to its breaking up. The latter seems the more probable 

 explanation, as threadlike ends are frequently seen in these stages 

 (fig. 17). This breaking-up appearance begins at one side of the 

 nucleus while the remainder still shows a close reticulum thickly 

 encrusted with chromatin (pi. 6, fig. 15; pi. 7, fig. 26). As the 

 breaking up proceeds further the rounded masses gradually disappear, 

 the chromatin apparently moving out along the threads which assume 

 a thicker, more compact appearance. 



As these threads become differentiated some evidences may be 

 found of a longitudinal split in each one (pi. 7, figs. 25, 27, 28). 

 This mav occur in some threads while the remainder are still emerging 



