BLACKMAN. — SPERMATOGENESIS OF THE MYRIAPOKS. 511 



somes lie near the centre and are arranged in nearly one plane, forming 

 an equatorial plate. Extending from the chromosomes toward the 

 poles are the linin fibres, which have now become mantle fibres. These 

 at first (Figure 2i») are comparatively short, but later they lengthen 

 (Figure 30) and extend about one half of the distance from chromo- 

 some to centrosome. They are much thicker than the astral rays and 

 stain much darker. The central spindle, or nuclear spindle, is entirely 

 distinct from the astral systems and lies in a clear area devoid of retic- 

 ulum, which represents the nuclear sap that has not yet become mixed 

 with the cytoplasm. The entire spindle is barrel- shaped, the fibres 

 converging slightly, but not coming to a point. At this time, and at 

 all later stages of mitosis, the fibres if continued through the cyto- 

 plasm would converge at the centrosomes, thus showing that these 

 small bodies, while not directly connected with the nuclear spindle, 

 still are the directing forces which determine its orientation and toward 

 which its fibres converge. 



During the late prophase and metaphase the astral systems continue 

 to develop, the rays becoming longer and more numerous. In the 

 equatorial region they may often be seen to cross, although this cross- 

 ing of the rays is not so pronounced as it is later during the anaphase 

 (Figure 32), at which time the archoplasmic structures reach their 

 highest development. In the metaphase (Figure 30) the centrosome 

 has often already divided to form the centres of the second division, 

 and this is always completed by the anaphase. The two centrosomes 

 are surrounded by the centrosphere just as in the prophase. The 

 lighter area of cytoplasm surrounding the centrosomes, however, is 

 usually much reduced by the time the spindle is completed (Figure 29), 

 and usually disappears entirely in the early anaphase. The cell mem- 

 brane in the region of the centrosomes is always depressed during meta- 

 kinesis and cytoplasmic cleavage (Figures 29-34). This depression first 

 becomes apparent in the late prophase at the time the outline of the ceU 

 is becoming rounded. This phenomenon probably has the same signifi- 

 cance as that ascribed to it in Scolopendra (Blackman, :05, p. 55). 



With the formation of the nuclear spindle the chromosomes, which 

 heretofore have been scattered throughout the nuclei, become lined up 

 near the middle of the spindle to form a fairly definite equatorial plate 

 (Figures 29, 30). While they do not all lie in exactly the same plane, 

 they are still arranged much more regularly than in Scolopendra. We 

 have seen that the characteristic form of the chromosomes in the late 

 prophase is that of a four-lobed structure, each lobe representing a 

 chromatid. The chromosomes in the equatorial plate are likewise 

 typically of this form, yet there are individual variations both in the 



