1919] Kofoid-Swezy: Trkhotujmpha. campanula 67 



Each chromosome consists of a long thread composed of chromo- 

 meres closely strung together (pi. 6, figs. 20-22; pi. 9, fig. 4-i). 

 In earlier stages these appear diffuse but later become more compact, 

 at the same time drawing together at the ends to form a loop (pi. 9, 

 figs. 46-49). These loops may appear coiled together (fig. 46) or 

 may preserve a V-shape. Both of these appearances may be seen 

 in the same nucleus (fig. 49). 



Soon after the appearance of definite chromosomes the flagellate 

 begins to round up, with an anterior migration of the nucleus (pi. 7, 

 fig. 31). This is followed by the splitting of the centroblepharoplast 

 and the separation of the two halves which remain connected hy the 

 darkly staining paradesmose (pi. 8, fig. 33). 



The nucleus at this stage is found a short distance below the base 

 of the dividing neuromotor system (pi. 7, fig. 30). The chronological 

 relation of the changes occurring in the nucleus and those of the 

 neuromotor apparatus vary considerably. The stages shown in figures 

 20 to 22, plate 6, usually occur before the centroblepharoplast divides, 

 yet occasionally the paradesmose may be fully formed before definite 

 chromosomes appear. The formation of the spindle fibers im- 

 mediately below the paradesmose does not occur until the nucleus 

 approaches the paradesmose with the nuclear membrane apparently 

 touching it. The spindle fibers are stretched between the dark masses 

 or centroblepharopla.sts at either end of the paradesmose (pi. 9, figs. 

 41, 43), but inside the nuclear membrane. When these are fully 

 formed the nuclear membrane is drawn out to a spindle shape with 

 the ends reaching the ends of the paradesmose (pi. 10, figs. 55-59). 

 The latter structure remains outside of the membrane but closely 

 pressed against it, usually partly imbedded within a fold, which in 

 many views gives it the appearance of occupying the center of the 

 spindle and chromosomes (pi. 10, fig. 55). In reality, however, the 

 chromosomes and spindle fibers are at all times completely separated 

 from it by the nuclear membrane. Its position thus approaches that 

 of the centrodesmose or central spindle of the metazoan cell. Since 

 it is outside of the nuclear membrane it is a paradesmose. 



With the beginning of the formation of spindle fibers or somewhat 

 earlier, another change takes place in the chromosomes, the loops 

 straightening out so that the chromosomes come to lie parallel to the 

 paradesmose. This process may be followed in figures 56 to 59, 

 plate 10, with the chromosomes in various stages of unbending. The 

 completion of this gives the equatorial plate phase (pi. 10, fig. 59), 



