214 Papers from the Marine Biological Laboratory at Tortugas. 



no relation between them and the syncytium other than one of close con- 

 tact. The syncytium has become exhausted and has come to form a narrow 

 fibrillar layer between them and the wall of the testis. This shrinkage of 

 the syncytium beneath the spermatoblasts is noticeable in much earlier 

 stages (figs. 9, lo, and ii). 



The growth of the nucleus keeps pace with that of the cytoplasmic body. 

 In the very young spermatoblasts the chromatin has the appearance of 

 irregular granules lying in a matrix of diffuse achromatic material. There 

 is always a karyosome present (fig. 8). Practically the same nuclear 

 structures are shown in figures 9 and 10 except that in the former the 

 karyosome was just above the plane of focus and in the latter the greater 

 portion of the nucleus was in the next section. The karyosome is very 

 persistent and constant in its appearance; in sections which have been 

 destained until the other structures of the nucleus have lost their stain, 

 the karyosome presents the appearance of a thick ring inclosing a lighter 

 colored substance. As the nucleus grows larger, there is an increase in the 

 amount of achromatin present and in the number of chromatin granules 

 (compare figs. 10, 11, and 12). 



The increase in the number of these granules is due, probably, to their 

 division. The subsequent growth of the resulting halves keeps them all 

 of a fairly constant size. When the nucleus has reached its maximum size 

 the chromatin granules begin to grow at the expense of the achromatin 

 (fig. 14). Their growth continues until they are as large or larger than the 

 karyosome, so that the latter becomes indistinguishable. Eventually, 

 practically all of the achromatin is absorbed and the chromatin granules 

 are retracted to the periphery of the nucleus, just beneath the membrane. 

 Here they undergo fusion to a certain extent and form large lumps of 

 chromatin, or karyomerites, of various sizes and shapes (figs. 16, 17, and 18). 

 The interior of the nucleus is filled with a colorless nuclear sap (fig. 17). 

 It is now ready to break down, but before describing this process it will be 

 well to consider the growth of the centrosome. 



The first indication of a centrosomal structure in the spermatoblast 

 appears at a very early stage, in the form of a distinct, darkly staining 

 centriole, from which two or three rays (fig. 8) pass out. The position of 

 this centriole, near the nucleus and in the proximal half of the cell, is in- 

 variable. The formation of a sphere around the centriole is not noticeable 

 until the latter has divided (fig. 9). In such a stage as this the sphere is 

 quite distinct and rays from both centrioles can be seen. It is impossible 

 to say whether the next stage (fig. 10) is reached by a division of the two 

 centrioles into four or by their fragmentation into a greater number. The 

 centrioles are very much smaller than they were and can not be counted 

 with any degree of certainty. The sphere has grown no larger and the 

 rays from the centrioles do not extend beyond its periphery. The centrioles 

 now lie in a homogeneous substance which fills the center of the sphere and 

 is more deeply staining than the latter. This substance represents the first 

 formation of the centrosome proper. 



