2i8 Papers from the Marine Biological Laboratory at Tortugas. 



as being phases of the centrosome subsequent to the stage shown in figure 15. 

 One cell alone showed an indistinct structure which might be taken for the 

 remains of a rapidly dissolving centrosome, but this can not be asserted to 

 be the ca"se (fig. 19). The body was round and apparently denser at its 

 periphery than in the middle and from it there passed off a number of short 

 and rather vague rays ; it was partially hidden by what is taken to be a large 

 mitochondrial body. The figure of it is not presented because much 

 importance is attached to it, but merely because it happened to occur in a 

 cell which was valuable for other features which it showed. All that is 

 definitely known to occur is that while the substance of the centrosome is 

 dissolved and disappears very rapidly, the centrioles themselves are un- 

 affected by the action. Having been freed, they scatter in small groups. 



The movements of the centrioles are hidden to a great extent, as it is 

 very difficult to establish their identity among the many and very small 

 mitochondrial and chromatic granules present. They eventually reach the 

 cell-membrane, however, either singly or in small groups, and here some 

 of them can be discerned quite readily (figs. 19, 24, and 25); others of 

 perhaps questionable identity can sometimes be seen in the interior of the 

 cell (fig. 19). A little later, secondary rays arise from those centrioles 

 which have reached the membrane, causing them now to become very 

 evident (figs. 21, 22, 26, and 27). Figures 21, 22, and 23 are consecutive 

 sections through the same cell, and that portion of the cell represented by 

 figure 21 showed the majority of the centrioles; those lay beneath the plane 

 of the focus figured. A few others were found in the next section of the cell 

 (fig. 22), but none were found in the upper section (fig. 23). It is thus seen 

 that the centrioles come to lie on the periphery in one half of the cell and 

 this half is the one which was originally proximal to the wall of the testis.^ 



The distribution of the centrioles was seen to better advantage in the 

 cell represented by figures 26 and 27. Here they were found entirely 

 confined to the left half of the cell. Those shown in the figures constitute 

 probably less than one-quarter of the total number in the cell, but only 

 those were figured concerning whose identity there could not be the slightest 

 doubt. The same thing may be said of figures 28 and 29 which represent a 

 slightly older cell. The centrioles are seen to have gathered into larger 

 groups and have moved closer together. From each centriole, too, there 

 has grown out a short flagellum. The rays from the centrioles were some- 

 what obscured on account of the "osmication" of the cell. These, however, 

 are well shown in figures 30, 31, and 32, which represent consecutive sections 



• The fact that this half of the cell is the originally proximalpne is easUy established in the case of such sper- 

 matoblasts as have never been forced away from the syncytium. Four facts must be borne in mind: (i) in 

 the young spermatoblasts the position of the centrioles is invariably in the proximal half of the cell; (2) matured 

 spermatoblasts which lie close to the wall of the testis are independent and are not a part of the shrunken 

 syncytium; (3) in such spermatoblasts the centrosome occupies a position distal to the wall of the testis; (4) 

 they undergo their later development in the same position. It is impossible to believe that the centrosome 

 and nucleus of these spermatoblasts have reversed their position during the growth of the cells. On the other 

 hand, in view of the fact that these cells usually lie free except at the point of contact with the syncytium, it 

 will be readily granted that the whole cell has probably revolved. Furthermore, a few instances of spermato- 

 blasts in various stages of growth have been observed, the position of whose centrosomes would indicate a turning 

 of the cell. Therefore, in these spermatoblasts, that portion which appears to be the distal half is really the 

 originally proximal one. After the disappearance of the centrosome in such spermatoblasts as lie close to the 

 wall of the testis, the centrioles come to lie beneath the membrane in the half of the cell directed toward the 

 lumen, that is, in the originally proximal half. 



