374 



Scientific Proceedings (124). 



process continues up to the metaphase of the first division, when 

 the chromosomes are fully condensed. The nuclear outline is 

 still persistent at this time and still exhibits an irregular contour, 

 conforming to that of the five bivalent chromosomes. 



Aside from the unusual nature of these processes, which, so 

 far as we know, have not hitherto been found in maturation stages, 

 two features appear to be of interest. First is the fact that as 

 the nuclear membrane (or the cytoplasm) pushes in around the 

 chromatin threads, it comes close to, but not in contact with, the 

 threads. This is easily seen, for the nucleoplasm is transparent 

 and the cytoplasm is dark, leaving the boundary, or nuclear mem- 

 brane, clear cut in outline. If the lobe is cylindrical, as is fre- 

 quently the case, the chromatin thread extends uniformly through 

 the center (or near the center), like a slender core. This condi- 

 tion, in which the chromosome is separated from the nuclear mem- 

 brane by a hyaline area of fairly constant thickness, is so uniform 

 and persistent (obtaining throughout most of the growth period) 

 that it can hardly be considered accidental. It suggests that 

 around the bivalent chromatin thread there may be a cortical 

 layer of dense or gelatinous material which holds off the nuclear 

 membrane. This layer, whatever its nature may be, is usually 

 from one to three times the thickness of the chromatin thread, 

 and varies with the latter through the growth period, becoming 

 thicker as the thread condenses. 



That the nuclear membrane is held off through the instru- 

 mentality of the chromosome itself is indicated by the fact that 

 the diameter of a lobe is usually greatest where the chromosome 

 lies, and that where the lobe extends beyond the chromosome 

 very far it becomes narrowed or closed. 



The second point of interest has to do with the fact that the 

 lobes of the nucleus, although often almost completely isolated 

 from one another, apparently never become cut off as separate 

 vesicles. Each seems to retain some connection, even if it is 

 only a narrow channel, with one or more of the other lobes, so 

 that the continuity of the nucleus is maintained. 



