iQoS] YAMAXOUCHI—SPOROGENESrS IN NEPHRODIUM 5 



being entirely free from such obstructions, and 



be 



The restin'g nucleus in the sporogenous tissue contains a chromatin 

 reticulum with one or several nucleoli. The general structure of the 

 nuclear reticulum needs mentioning. It does not seem to consist of 

 two distinct elements, chromatin and linin, with chromatin granules 

 distributed irregularly upon or imbedded in the linin ground-sub- 

 stance, but it seems to be composed entirely of chromatin material- 

 The appearance which indicates that there may exist a mixture of 

 two substances — the dark-stained mas^s and light-colored strands — 

 does not seem to be due necessarily to a different affinity for stains, 

 but to the fact but that the more compact regions of chromatin 

 material are more affected by stains than the more loosely aggregated 

 regions, which are lightly stained. 



ms no rule 



sometimes 



to the membrane and sometimes they are centrally located. The 

 form is rounded in most cases, but often they are aggregated into one 

 or two irregular masses. Even in the resting nucleus they show a 



vacuollzed structure. 



The chromatin reticulum in the resting nucleus is irregularly dis- 

 tributed, often great masses being located in the center or sometimes 

 eccentric near the periphery, leaving the center vacant. Approach- 

 ing the prophase, there seems to be a tendency of some of the chroma- 

 tin material to form a continuous spirem, L e., some fine strands of 

 the chromatin may break apart entirely or may become thicker by 

 getting the material from some ragged chromatin clumps which con- 

 sequently diminish in size. The sph-em, uneven at first, becomes 

 oraduallv uniform in thickness and distributed throughout the nuclear 



o 



cavity {jig. 2). "Wliether there is present a single spirem or not was 

 not determined. Close examination of this stage in a number of 

 preparations showed that it was hardly possible to make out free ends, 

 and this may be taken as an evidence that the spirem is a continuous 

 one. Nucleoli persist in positions distinctly isolated from masses of 

 the chromatin reticulum, so that they do not seem to contribute to 

 the establishment of the spirem through the migration of material. 

 Usuallv at this stase thev seem to unite into (me mass. 



