SPECIAL NUCLEAR PHENOMENA. 39 



disk-shaped center and the chromatin systems have become intimately 

 intermingled, though there is still evidence for some time of the presence 

 of a greater number of threads in the combined chromatin masses than 

 were present in either of the fusing masses. The nucleoles combine 

 into a single homogeneous nucleole of approximately twice the volume 

 of either of those which combined. The process of union so far has 

 gone on rather rapidly ; at least there is no evidence of increased size 

 in the entire perithecium between the stages when the fusion begins 

 and the time when it is completed. The nucleus thus formed is the 

 so-called primary nucleus of the ascus. 



The ascus has reached about half its mature dimensions at this 

 stage, but the whole perithecium is rather more than half grown. As 

 noted, the penicillate cells have begun to develop, but the characteristic 

 bulbous-based, spine-like appendages are not yet present. A relatively 

 long period now ensues, leading up to the spirem stage in the prophases 

 of the first division. The nucleus during this period grows with the 

 growth of the ascus and also undergoes characteristic changes, part of 

 which constitute essential stages of the fusion process. 



In the nuclei at the time of fusion, and immediately thereafter, the 

 chromatin substance extends through a large part of the nuclear cavity 

 (fig. 39), as was described above for the stage preceding fusion. The 

 chromatin threads are still abundantly connected by fibrillse, and these 

 seem to become more numerous and delicate, so that their outlines can 

 scarcely be made out and the chromatin strands appear as if they were 

 embedded in a more faintly stained ground substance. As a result the 

 threads become progressively more difficult to follow, and it is less easy 

 to count them. The whole chromatin mass now begins to contract and 

 becomes more dense (fig. 43). This contraction is always away from 

 the antipolar region and toward the center, as if a contraction of the 

 threads had taken place by which they are drawn up to their points of 

 attachment in the center. The antipolar region is thus left almost free 

 of stainable materials except for the large red-stained nucleole. With 

 the completion of this stage of contraction the threads may become more 

 plainly visible (fig. 44), but they are much shorter. Frequently the 

 free ends of the threads stick out from the denser mass and are plainly 

 shown, at this stage at least, not to be connected as loops at their anti- 

 polar extremities (fig. 44). Occasionally a thread may extend from 

 the mass as far as the nucleole. 



There is evidence in some cases also of the presence of a consid- 

 erable amount of faintly stained thready material which may appear in 

 section, extending from the surface of the denser mass as a sort of 



