36 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



tributed throughout the vacuole (Fig. 39). They lose their homogeneous 

 appearance and sharp outlines and assume a granular condition. When 

 the constriction of the cell is completed, the nuclear membrane has also 

 reappeared (Fig. 39). 



Even during the late anaphase the cell membrane in the region of the 

 equator of the cell has become depressed, thus indicating the beginning 

 of the division of the cytosome. This depression continues to deepen 

 (Fig. 37), until it becomes very evident that it is in reality an annular con- 

 striction which is slowly dividing the cell into two approximately equal 

 parts (Fig. 38). The division of the cell body is very different from that 

 usually occurring in the male cells and in all well-differentiated cells, but 

 is in many respects identical with that occurring in the cleavage of the 

 ovum. It is very evident that the division is not accomplished by the 

 mere formation of a single intervening wall between the cells, as is said 

 to be the case in vegetable cells and in some animal cells, for at all stages 

 two membranes can be readily distinguished (Figs. 38, 39), and at the 

 bottom of the constriction it is plainly seen that these two walls are 

 continuous, — i. e. are formed by the mere forcing in of the cell mem- 

 brane ( Fig. 38). During the progress of this division the reticular 

 matrix of the testis which surrounds the spermatocytes of the large type 

 in a thick layer presses into the constriction and completely fills the 

 cavity thus produced (Fig. 38). 



During the anaphase the archoplasmic structures of the cell are more 

 marked than at any other time. The astral rays are very numerous and 

 seem to penetrate to every part of the cell. But those which extend 

 toward the equator are both more numerous and more conspicuous than 

 those of any other region (Figs. 35, 36, 37). In many cells they 

 seem to connect the centrosomes with the cell wall in the region of the 

 equator of the cell. When we consider the behavior of the same 

 structure in the other type of spermatocyte, this view would appear to be 

 justified. However this may be, during the subsequent formation of the 

 Zwischenkorper, the astral rays still persist as such, still apparently 

 attach to the constricting cell membrane, and most certainly take no 

 part in the formation of the persisting spindle. 



During the telophase the interzonal filaments are collected together into 

 a bundle by the constricting membrane and form a very well-developed 

 Zwischenkorperchen. At first the fibres composing this are quite 

 long and extend from the plane of division about half the distance to 

 the nuclei. Later, however, when the row of central granules appears, 

 they decrease in size. These central granules are at first small bodies 



