Papers from the Marine Biological Laboratory at Tortugas. 215 



Further multiplication of the centrioles is accompanied by their separa- 

 tion from each other and by the spreading of the substance of the centro- 

 some (figs. 11 and 12). It becomes very difficult to distinguish the indi- 

 vidual centrioles from the substance in which they lie, but several of them 

 can usually be seen lying at various points on the edge of the centrosome. 

 The outer sphere, too, has increased in size and about this time begins to 

 resolve itself into an outer dark court and an inner clear court (fig. 12). 

 A little later on, the centrosome, which is now considerably larger, becomes 

 spherical and acquires a definite membrane and the rays become stronger 

 and stronger (fig. 13). It reaches its full growth at approximately the same 

 time as does the nucleus (fig. 14). From it there passes out in all directions 

 a great number of strong rays, which extend to all parts of the cell; at the 

 base of each lies a small centriole. Lying around the centrosome on all 

 sides, but more particularly on the sides away from the nucleus, is a mass 

 of mitochondrial granules (figs. 14 and 15). They are irregular in shape and 

 size and stain deeply with iron ha^matoxylin. Figure 14 does not show all 

 the mitochondria that were seen in the cell. 



The formation of the mitochondria is rather sudden. They appear in 

 the sphere shortly after the formation of the inner court and are found at 

 first on all sides of the nucleus. Figure 13 represents approximately the 

 stage at which they first appear; it was drawn from a cell which showed the 

 efifects of osmic acid to some extent and therefore does not represent either 

 the mitochondria or the rays as fully as they might be seen in other cells. 

 As the mitochondria increase in number and size, they gradually obliterate 

 the outer court of the sphere, while the inner court grows wider and wider. 

 The last traces of the outer court are shown in figure 15. With the appear- 

 ance of the mitochondria, one loses sight of that body which was mentioned 

 as being found in the cytoplasm of the young spermatoblasts (figs. 8 to 12). 

 This body gradually grows larger and very pronounced, but later on it is 

 impossible to distinguish between it and any of the larger mitochondrial 

 granules. 



Judging from the great number of cells which are found with a fully 

 formed centrosome, the last stage in the growth of the spermatoblast must 

 extend over a very long period. Gradually the mitochondria withdraw from 

 the space between the centrosome and the nucleus and that half of the 

 centrosome which lies toward the nucleus becomes more lightly staining 

 and seems to lose its definite outline. On the other hand, the opposite half 

 of the centrosome takes a deeper stain and it can actually be seen that the 

 centrioles are massing themselves upon that side (fig. 14). At this time, 

 one or two comparatively large granules are to be found in the centrosome; 

 they are very constant in their appearance but no suggestion can be made as 

 to their significance. Finally, those rays which traverse the space between 

 the centrosome and the nucleus attach themselves to the nuclear wall 

 (fig. 14) ; then follow, in quick succession, the retraction of the chromatin 

 to the wall of the nucleus, the dissolution of the latter on the side toward 



