106 PROCEEDINGS OF THE AMERICAN ACADEMY. 



shown by Meves in bis Figure 2, wbere the elongated nucleus with its 

 contained spindle figure is entirely isolated from the two centrosomes 

 of the cell. Apparently he has overlooked the fibrous prolongations 

 which connect the ends of the spindle with the centrosomes. The 

 coarse, granular, extranuclear fibres already referred to are still to be 

 seen occupying the greater part of the cell, extending in somewhat 

 irregular sinuous courses outside the nucleus firom pole to pole. 



The mitotic figure here described is evidently that of the first 

 spermatocyte division ; but now a peculiar phenomenon occurs. 

 Instead of a division of the chromosomes taking place, as would be 

 expected, the figure does not for the present progress beyond the 

 beginning of the metaphase. The spindle fibres either break down, 

 or, what is more likely, become closely pressed together into a single 

 bundle ; but the chromosomes maintain their form for some time. A 

 cross section through the middle of the spindle at this stage (Figure G) 

 shows the chromosomes still surrounded by a nuclear membrane, and 

 likewise the cut ends of the cytoplasmic fibres lying outside that 

 membrane. 



The interzonal body persists throughout the period of the nuclear 

 changes last described without any apparent alteration in form or size, 

 but toward the end of this period it has a position at, or very close to, 

 the proximal end of the cell, and soon afterward it is found directly 

 beneath the proximal centrosome. Eventually it occupies the base of 

 the finger-like process of cytoplasm (Figure 9) previously described. 

 There is some variation in the sequence of phenomena during this 

 period. As early as the stage shown in Figure 7, the centrosome and 

 the interzonal body are sometimes seen closely applied to each other, 

 while in other cases at a much later stage in the nuclear metamorphosis 

 (Figure 9) a portion of the finger-like process may still be seen between 

 the two. At length the interzonal body occupies the place of the 

 finger-like process of cytoplasm and protrudes from the main body of 

 the cell (Figure 10), the centrosome continuing to occupy its former 

 position at the proximal end of the projection. At this stage the in- 

 terzonal body is a spherical object supported on a cylindrical process 

 of the cell, and resembles superficially the first polar cell formed 

 during the maturation of eggs ; but it differs from the polar cell in 

 obvious particulars. Not only is it destitute of visible chromatic 

 substance and the usual remnants of interzonal filaments, but it 

 exhibits from the beginning a fairly well-defined outline on the side 

 toward the body of the cell. Except for the persisting centrosome, 

 its substance is homogeneous and slightly more refi"active than the 

 neighboring cytoplasm. 



