SPECIAL NUCLEAR PHENOMENA. 41 



contraction (figs. 43-47) are magnified only by 1,000, while the figures 

 of the earlier stages, Nos. 31-34, are magnified by 1,500. 



The spirem figure becomes still more definite with the further 

 growth of the nucleus and the ascus till, at a stage when the penicillate 

 cells are well started in their development and the perithecium is nearly 

 full-sized, the ascus nucleus reaches its full size and we get such spirem 

 stages as those shown in figs. 48 and 49. The nuclear structures at 

 this stage are very sharply defined. In these figures I have brought all 

 the threads into the plane of the median optical section of the nucleus, 

 representing those that lie above as darker and those below as lighter 

 and fainter. This makes the figures appear much more crowded and 

 confused than they really are in the preparations. The center is a disk 

 lying on the outer surface of the nuclear membrane, frequently in a 

 slight depression, and from it very sharply differentiated threads pass 

 back and can be traced with the greatest ease into the antipolar region. 

 There is practically no stainable interfilar substance; the threads lie in 

 an unstained nuclear cavity, with nothing to interfere with the sharpness 

 of their outlines. As in earlier stages, two extremes as to the distribu- 

 tion of the threads in the nuclear cavity can be distinguished. In the 

 one case some of the threads follow rather closely the inner surface of 

 the nuclear membrane and others pass more directly to the antipolar 

 region through the midst of the nuclear cavity. This results in a fairly 

 even distribution of the chromatin material in the nucleus (fig. 49). In 

 the other case all or most of the strands pass from the central body 

 through the middle of the nuclear cavity, forming a spreading bundle 

 or irregular cone (fig. 48), and then spread out in the antipolar region. 

 Frequently at this stage, as at earlier stages, the whole bundle may be 

 spirally twisted. 



The antipolar ends of the threads are frequently seen to be free. 

 In other cases they are in contact with each other, giving the appear- 

 ance of being fused or continuous. Not infrequently they are in contact 

 with the nucleole. The end region of a thread may lie on the surface 

 of the nucleole for a short distance, but there is never any indication 

 of a fusion of the substance of the chromatin thread with that of the 

 nucleole. The nucleole is a sharply defined oval body, and the ends 

 of the threads appear to be merely in contact with it. 



Superficially, perhaps, the nucleus at this stage bears little resem- 

 blance to the spirems figured by Rabl and Flemming for the salamander, 

 or by Strasburger for the endosperm nuclei of Fritillaria and the pollen 

 mother cells of the lily, but there can be no question that this is a spirem 

 stage corresponding to spirems in the cases mentioned and that in the 



