156 CHAS. W. METZ AND JOSE F. XOXIDEZ. 



Little or no regularity of plan is to be seen in the configuration 

 of the nucleus. Its shape is varied and often bizarre. Appar- 

 ently the lobes ramify at random, following the contour of the 

 long, more or less twisted threads. The nucleolus usually lies in 

 a lobe or pocket by itself, or in a chamber at the junction of two 

 or more lobes. 



The lobes themselves are of various shapes, flat, pocket-like 

 sheath-like, cylindrical, or of intermediate sorts. It is to be 

 noted, however, that all of the nuclei undergo the same series of 

 changes and show essentially the same features. There is no 

 irregularity in this respect. 



The maximum of distention and distortion of the nucleus is 

 reached soon after the process begins, and while the chromatin 

 threads are long and slender. At this time the lobes are so 

 attenuated and slender that the nucleus is almost lost to view. 

 For the most part it can only be seen as narrow, winding channels, 

 ramifying through the cytoplasm. These channels often extend 

 almost or quite to the periphery of the cell. Since each channel 

 usually contains a single (bivalent) thread, the threads thus be- 

 come almost completely isolated from one another. 



Subsequently the threads undergo a gradual condensation, and 

 the lobes a coincident contraction, as growth progresses (Figs. 



5-9)- 



When the detailed structure of the lobes is examined, at any 



stage, it is seen that almost invariably the deeply staining chro- 

 matin thread (chromosome), extends through the center of the 

 hyaline lobe like a core, if the lobe is cylindrical, or lies midway 

 between the sides, if the lobe is flat. It is separated from the 

 membrane by a transparent layer of approximately uniform thick- 

 ness. The structure might be likened to an insulated wire, in 

 which the chromosome represents the wire and the hya|ine region 

 the insulation. 



As the lobe is followed beyond the chromosome it is seen to 

 become narrow or closed. The maximum thickness is almost 

 always in the region occupied by the chromosome. This suggests 

 that the chromosome is surrounded by a cortex of dense or gela- 

 tinous material which holds off the nuclear membrane. 



NO . --! Mil ,! ( haiige in tlu-sr conditions is I" l>r "1 >-IT\ vl as 

 the chromosomes condense and the lobes contract. The two 



