212 



MAULSBY W. BLACKMAN. 



During the metaphase, however, one of the chromatic ele- 

 ments does not show the dumb-bell-shape characteristic of the 

 rest, but is very evidently a rod split in the opposite direction, 

 /. e., longitudinally. This peculiarity is also to be seen in the 

 preceding prophase where the accessory chromosome is of the 

 same shape as in the first spermatocyte prophase. As it is seen 

 during the early metaphase, this element is arranged with the 

 plane of cleavage at right angles to the spindle (Fig. 20), but 

 upon the contraction of the mantle fibers which are attached to 







FIG. 20. X 9 dia. Metaphase of second spermatocyte. The difference in shape 

 and orientation existing between the accessory and the other chromosomes is evident. 



FIG. 21. X l>9 2 dia. High magnification of same stage, showing the differences 

 exhibited by the accessory chromosome in the relation of the chromatids and in the 

 attachment of the mantle fibers. 



FIG. 22. X 1,920 dia. Slightly later stage ; showing the effect of the contraction 

 of the mantle fibers on the orientation of the accessory chromosome. 



opposite ends of the erement it revolves through an arc of 90 

 (Figs. 21, 22) and the component chromatids as they are pulled 

 apart seem to glide over each other (Fig. 22) in a manner similar 

 to that already noted as characteristic of the ordinary chromo- 

 somes during the first mitosis. 



It will be seen by consulting the accompanying figures that 

 the behavior of the other elements is quite different. These are 

 arranged with their long axis parallel to that of the spindle, the 



