BIGELOW : NUCLEAR CYCLE OF GONIOXEMUS MUEBACHII. 305 



ness of the reticulum and the size of its karyosomes (Fig. 20). The 

 chromatin masses surrounding the nucleolus decrease in number until it 

 is clearly visible that they are attached to the periphery of a distinct 

 plasmosome (Fig. 20), and that each one lies at the point of origin of 

 one of the limn strands. This change is accompanied by a progressive 

 increase in the thickness and staining capacity of the strands ; and the 

 evidence seems to show that the chromatic granules of the nucleolar 

 shell migrate outward along the course of the achromatic fibres. At 

 about this time the karyoplasm disappears, leaving the nucleus filled 

 merely with transparent fluid, and simultaneously it is seen, on Auerbach 

 preparations, that the karyosomes have changed their chemical reaction, 

 being now no longer basic but acid. This change is exactly the same 

 that occurs in somatic cells at a similar stage, and has already been dis- 

 cussed (see page 32). The spermatogonium now presents the appear- 

 ance represented in Figure 21. The network is stout, while the number 

 of meshes appears to have decreased somewhat; a varying number of 

 chromatin masses are still attached to the periphery of the nucleolus, 

 while the karyosomes lying at the nodes stain strongly with iron haema- 

 toxylin, and are more prominent and sharply outlined. Their number 

 is very considerable, but seems to vary somewhat in different cells ; and 

 since they vary also greatly in size, outline, and composition, being either 

 dense or granular, I believe that they do not represent discrete chroma- 

 tin structures, but merely aggregations of chromatic microsomes collected 

 along the course of the achromatic network. In many ways they recall 

 the appearance and behavior of the very much more numerous karyo- 

 somes seen in the nuclei of oocytes in the latter part of the growth 

 period, which afterward fuse to form the chromatic segment (see page 

 34G-347). 



The karyosomes now become massed along the net strands, thus form- 

 ing definite chromatic segments, which are separate from one another, 

 yet stand in connection through the persistent linin strands (Figs. 20, 

 22). At first, as in the cell shown in Figure 20, there may be only one 

 or two such segments ; but they increase in number until eventually the 

 entire net consists of such beaded segments. I have been unable to 

 determine that there is an invariable number of segments, while the 

 number of karyosomes taking part in the formation of each segment 

 appears to vai'y from two to four or five. The fact that these changes 

 are not precisely synchronous in all parts of the same nucleus is a great 

 help to their true interpretation, for, as is the case in the cell repre- 

 sented in Figure 20, sevei'al successive stages — in this case, both sepa- 



VOL. XLVlll. — no. i 20 



