BLACKMAN : THE SPERMATOGENESIS OF SCOLOPENDIU. 41 



that one daughter cell contains seventeen chromosomes, while the other 

 possesses but sixteen (Figs. 39, 41). 



At the opening of the prophase of the second spermatocyte the sixteen 

 ordinary chromosomes are of a granular consistency, although their form 

 is so definite that there can be no question of their individuality. They 

 have the appearance of short rods of diffuse chromatin the centre of each 

 of which is slightly constricted, thus producing a dumbbell-shaped body 

 (Figs. 41, 42). In the succeeding stages these become more dense, and 

 finally go to the equatorial plate as homogeneous bodies of a distinctly 

 bilobed form. The chromosomes are rather closely crowded within the 

 small nucleus, and there does not seem to be any large amount of linin. 

 When arranged in the equatorial region (there is no true equatorial plate 

 any more than in the first division), the lobes of these bodies are directed 

 toward the poles of the spindle, thus giving basis for the conclusion that 

 we have here a cross division of the chromosome. 



Meantime the changes occurring in the archoplasmio structures inci- 

 dent to the formation of the spindle are rather unusual. The centro- 

 some with its surrounding asters does not leave its position upon the cell 

 membrane, but separates and moves apart along this structure. As the 

 migration continues (Fig. 41), the surrounding astral rays become more 

 numerous and at the same time more definite, and they extend farther 

 into the cytoplasm. During the progress of this migration the cell wall 

 in the region of the centrosome is pushed outward, possibly by the 

 growth of the astral fibres (Fig. 41). This process continues until the 

 astral systems have reached points upon the cell membrane at opposite 

 poles of the nucleus, so that a plane drawn through the two centrosomes 

 would bisect this vesicle (Fig. 42). At this time the astral rays upon the 

 side of the centrosome nearest the nucleus are continuous with the similar 

 rays from the other centrosome, thus forming a spindle the rays of which 

 pass over the still persisting nuclear membrane. When the nuclear mem- 

 brane finally disintegrates, the centrosomes, still close to the cell mem- 

 brane, have arrived at opposite poles of the cell, and the rays extending 

 from them penetrate all portions of the cytoplasm. Those which were 

 seen to be continuous and to pass over the nuclear membrane become, 

 upon the disintegration of this structure, attached to the chromosomes 

 and serve as mantle fibres. Those of the two astral systems which 

 proceed from the centrosomes in other directions remain distinct. 

 This is very well shown at the stage represented in Figure 43, where 

 those from the two poles, proceeding in a line diagonal to the long 

 axis of the spindle, cross in the equatorial region and can be readily 



