BIGELOW: NUCLEAR CYCLE OF GONIONEMUS MURBACIIII. 327 



pear as homogeneous masses, distinguished from the surrounding cyto- 

 plasm by the fact that they stain more deeply, are distinctly outlined, 

 and totally lack the reticulate structure of the latter. 



Staining with iron haematoxylin, either alone or followed by a plasma 

 dye, is unsatisfactory for the study of the archoplasm. The most suc- 

 cessful stains for differentiating this substance are the safranin-gentian 

 violet dye, and iron haematoxylin followed by the iodide-iodine solution 

 mentioned on page 290. 



The centrosome at this stage appears as a black granule without any 

 trace of surrounding sphere, lying at the margin of the cell. The tail 

 filament, now always present, seems to arise from the centrosome, and is 

 about equal in length to the diameter of the cell (Fig. 90). Whether or 

 not this filament actually grows out from the substance of the centro- 

 some is best discussed later, in connection with the "giant" and " mul- 

 tiple " spermatids. From this point on, important modifications rapidly 

 occur in nucleus, centrosome, archoplasm, and cytoplasmic cell body. 

 The centrosome, confining our attention for the present to this structure, 

 is in all earlier stages a single dense granule, lying at the margin of the 

 cell, opposite the broad side of the oval nucleus. During the progress 

 of metamorphosis it migrates around the margin of the cell until finally 

 it comes to lie in the prolongation of the long axis of the nucleus. This 

 migration, however, is not completed until much later, only its com- 

 mencement being shown in Figures 90 and 91. At the same time it in- 

 creases somewhat in size (Plate 5, Fig. 92), and a delicate, deeply stain- 

 ing filament can be detected extending from it inward along the axis of 

 the cell toward the nucleus. As in the case of the axial filament of the 

 tail, it is perhaps doubtful whether this actually grows out from the 

 substance of the centrosome, or whether it represents a modification of 

 cytoplasm metamorphosed under the influence of that organ. The cen- 

 trosome now divides into two equal, minute, black granules, which may 

 at first lie, as Gorich (: 03*, : 04) found in Spongilla and Aurelia, side by 

 side at the margin of the cell, but very soon they take up a position 

 radial to the cell (Fig. 93). These two bodies are still closely in contact, 

 and it is only by careful focusing that their double nature can be de- 

 termined. The axial filament now extends from the proximal centro- 

 some inward nearly to the nuclear membrane, and this centrosome now 

 migrates inward along the filament, as is shown by comparing Figures 93 

 and 94 ; in Figure 94 it is seen to lie about halfway between the nucleus 

 and the distal centrosome, with which it is connected by the filament. 

 Eventually it reaches the nuclear membrane and for a long time can be 



