2i6 Papers from the Marine Biological Laboratory at Tortugas. 



the centrosome, the scattering of the karyomerites, and the disappearance 

 of the centrosome with its rays. 



The actual beginning of dissolution of the nuclear wall is shown in 

 figures 15, 16, 17, and 18; these go in pairs, figure 15 with figure 16 and 

 figure 17 with figure 18, representing consecutive sections through two 

 different cells. In figure 15 the mitochondria lie for the most part above 

 the centrosome, while the latter in turn is at a slightly higher focus than 

 the karyomerites. These last, represented in the figure as large black 

 bodies, lie free in the cytoplasm, into which also some of the nuclear sap 

 has escaped. Many of the mitochondria have grown into short stout rods 

 (chondrioconts). It will be noticed that the rays from the centrosome are 

 becoming less evident. In figure 16 is shown the remainder of the nucleus; 

 some of the nuclear sap and a few of the karyomerites are moving out 

 into the cytoplasm. The further and complete scattering of the karyo- 

 merites is usually accompanied by the total disappearance of the centro- 

 somal rays. But in figures 17 and 18 a cell is shown in which absolutely 

 no traces of the centrosome or the rays could be found and as yet none of 

 the nuclear material had escaped into the cytoplasm. 



These figures were drawn very carefully and show all the structures 

 visible in the cell. The mitochondria were rendered somewhat indistinct 

 by the action of the osmic and acetic acids, but the same can hardly be 

 said of any surviving centrosomal structure; for a younger spermatoblast 

 lying beside this cell showed a distinct centrosome. The nuclear membrane 

 has become very much thinner and at one place, on the side towards the 

 mitochondrial apparatus, it has been dissolved (fig. 18). It would therefore 

 seem that the same process, undoubtedly a chemical reaction, which brings 

 about the disappearance of the centrosome also leads to the dissolution of 

 the nuclear membrane. Of the two phenomena, the latter is completed 

 the more slowly. The karyomerites are carried to various parts of the cell 

 with the diffusing nuclear sap. 



The greater part of the chromatin remains in what was originally the 

 distal half of the cell, although some of the fragments move into the region 

 occupied by the mitochondria. This distribution of the chromatin is 

 illustrated in figures 19 and 20, which represent two consecutive sections 

 through the same cell. That part of the cell shown in figure 19 constitutes 

 the proximal half of the cell, while the distal half is shown in figure 20. 

 The larger lumps of chromatin now break down into several smaller parts 

 (figs. 20 and 22), and as a result of this fragmentation there is a more equal 

 distribution of the chromatin throughout the whole cell (figs. 24 and 25, 

 consecutive sections through the same cell) . The ultimate karyomerites show 

 an extreme variation in size, some of them being extremely small (fig. 22). 



Kuschakewitsch ('11) has described a somewhat similar formation of 

 karyomerites in the apyrene cells of Vermetus. Here the karyomerites 

 apparently are all fully formed before the dissolving of the nuclear mem- 

 brane. They are of a fairly uniform size and shape and many of them show 



