42 bulletin: museum of comparative zoology. 



traced to the cell membrane itself. It is surprising how clear and 

 distinct the archoplasmic structures are at this stage, when we re- 

 member that during the preceding telophase much of the archoplasm 

 was lost by the destruction of the spindle remnants at the time of the 

 rotation of the cells (Fig. 41). 



During the prophase the alterations in the character of the cytoplasm 

 are very similar to those already observed in the first spermatocyte. At 

 the beginning of this division the cytoplasm shows the same reaction to 

 stains due to the dissolution of the astral rays and their deposition in 

 the hyaloplasmic areas, for while the material composing the spindle rem- 

 nants is lost to the cell, that derived from the astral systems is of course 

 retained. During the course of the prophase we see the same progres- 

 sive change in the staining l'eaction of the cytoplasm as in the first mat- 

 uration division, and this progresses at the same rate as the formation of 

 the astral rays. This is clearly seen when we compare Figures 41, 42, 

 43. In Figure 42 that pai't of the cytoplasm not yet involved in the 

 astral systems shows the dense close-meshed structure characteristic of 

 all the cytosome at an earlier stage (Fig. 41), while the part in which 

 the astral rays are to be seen is much clearer. In the metaphase (Fig. 

 43) all of the cytoplasm is transparent and has resumed its usual reticu- 

 lar appearance. 



During the pi*ophase the cell is always of an oval shape (Figs. 41, 

 42), with the long axis parallel to that of the follicle, but at the time 

 of the beginning of the metaphase the outline is more nearly spherical, 

 and very often the shorter diameter of the cell is that connecting the 

 two centrosomes. This is rather extraordinary, for, as we shall see pres- 

 ently, the cell later elongates in the axis of the spindle (Figs. 44, 45). 



We have seen that, at the beginning of the metaphase, the dumbbell- 

 shaped chromosomes are arranged with the two lobes directed towards 

 opposite poles of the spindle (Fig. 43 and Figs. D, E, F). At this 

 stage, however, one of the chromatic elements does not show the shape 

 characteristic of the others, but is very evidently a rod split in the op- 

 posite direction, i. e. longitudinally. This peculiarity was also seen in 

 the preceding prophase, where the accessory chromosome is of the same 

 shape as in the first spermatocyte prophase. As seen during the early 

 metaphase, this element is arranged with the plane of cleavage at right 

 angles to the spindle axis (Fig. D), but upon the contraction of the 

 mantle fibres, which are attached to opposite ends of the element, it re- 

 volves through an arc of ninety degrees (Figs. E, F.), and the component 

 chromatids as they are pulled apart glide over each other in the manner 



