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Mr. L. Hogben. 



inevitable if the arc-shaped chromosomes of the anaphase are to retain 

 the same axis of symmetry with respect to the achromatic spindle during 

 the process of attenuation. As the telophase filaments become more 

 elongated, their arrangement becomes increasingly more difficult to follow 

 (figs. 5, 6). The chromatic filaments, however, at all stages remain in 

 contact with the nuclear membrane ; whereas the plasmosome, which may 

 appear early in the telophase, while the individual chromosomes are still 

 identifiable as such, is always seen to be in the centre of the nucleus. 

 There is thus no justification for regarding the plasmosome as in any way 

 connected with chromatin organisation of the nucleus. 



If the history of the prophase chromosomes is traced chronologically 

 backwards, it is seen that their earliest precursors that can be definitely 

 identified are in the form of attenuated, finely-beaded and convoluted 

 filaments. As these become abbreviated, they show at first a definite 

 orientation with respect to the plasmosome (figs. 7-10). At no stage either 

 in prophase or in telophase is there any justification for regarding the 

 individual filaments as united in a continuous spireme. The history of the 

 chromosomes in the prophase recapitulates in obverse sequence the behaviour 

 of their representatives in the preceding telophase. In this essential, the 

 facts are in agreement with the conclusions drawn by Digby as regards 

 Osmunda, 1919. But there is no evidence of cleavage for the ensuing 

 metaphase, until the prophase chromosomes begin to assume the arc-shaped 

 contour characteristic of the anaphase (figs. 9, 10). There is only one stage, 

 of comparatively brief duration, in the germ nuclei of Libellula, when the 

 individuality of the chromosomes is obscured ; this is the so-called reticulate 

 stage, or, as Bolles Lee has called it, the spiropliase ; and it will be noticed 

 that there is no reason to infer that the individuality of the chromosomes is 

 interrupted at this point. On the contrary, the phenomena described would 

 more naturally lead to the conclusion that the spiropliase is in reality merely 

 that point in the nuclear cycle, when the chromatin filaments become so 

 elongated, and the chromomeres so widely separated that current inethods of 

 observation can no longer detect the direction of individual strands. 



The only recent account of the behaviour of the chromatin organisation of 

 the nucleus during interkinesis on the Hexapoda is given by Schaffer, 1919 (8). 

 In Lachnosterna (Coleoptera), " the chromosomes spin out into fine chromatic 

 threads, and, as the nucleus grows, the threads become more and more 

 complex . . . this resting nucleus is of relatively short duration, for soon 

 the chromatin begins to condense into heavier threads." One very important 

 resemblance between the events of the nuclear cycle in Libellula and 

 Lachnosterna will be described later. While in general the few workers 



