BLACKMAN. — SPERMATOGENESIS OF THE MYRIAPODS, 509 



the cell membrane, and finally take up their position on the inner face 

 of this structure. In this migration they do not move in opposite 

 directions, but proceed toward the side of the cell nearest to a line 

 connecting the two centrosomes. Thus when they reach the cell 

 membrane they usually both lie upon one side of the cell, which as yet 

 still preserves its rectangular outline (Figures 24, 25). During this 

 migration the nucleus also undergoes a movement in a similar direc- 

 tion, seemingly striving to retain its position in a line between the two 

 centrosomes. Thus at a time when the centrosomes have reached the 

 cell membrane, the nucleus lies very near to the same side of the cell, 

 as is shown in Figure 25. When the centrosomes come in contact 

 with the membrane, they immediately begin to move apart along its 

 inner face until they have reached opposite poles of the cell, the nu- 

 cleus meantime changing its position so as to lie between the two 

 (Figure 24). 



Meanwhile the centrosomes have changed considerably in appear- 

 ance. By the time they have reached the cell membrane each is en- 

 closed in quite a distinct centrosphere. This is homogeneous or finely 

 granular, and stains slightly darker than the cytoplasm (Figures 24, 

 25). The astral rays have increased both in size and number, and 

 now penetrate to nearly all regions of the cytoplasm. Those from the 

 two poles may be distinctly seen to cross one another near the centre of 

 the cell (Figures 24, 25), although this crossing is not so apparent as it 

 is later (Figure 28). These fibres are entirely distinct from the cellu- 

 lar network, as the cytoplasmic reticulum is still evident except in the 

 regions immediately surrounding the poles. In these regions, how- 

 ever, the network seems to have entirely broken down, leaving only 

 the hyaloplasm and the penetrating astral rays. Thus each centro- 

 sphere is surrounded by a transparent area of considerable width 

 (Figures 24, 25), which serves as an excellent background for the cen- 

 trosome and centrosphere. Appearances similar to this have been 

 observed in other m)a'iapods by Meves und von Korff (:0l), P. Bouin 

 (:00, :01), and Medes (:05). 



During the time of the divergence of the centrosomes upon the cell 

 membrane the cell has altered considerably in shape. In the vesicle 

 stage and early prophase the cells are typically rectangular in outline. 

 Now, however, they undergo a change by which their form becomes 

 approximately spherical. This I believe to be directly due to the ap- 

 pearance and development of the archoplasm (Blackman, :05), for the 

 rounding off of the cell is only perfected when the astral systems have 

 reached the height of their development (Plate 2, Figures 28-30). 



The achromatic changes thus far described have been entirely inde- 



