598 MR A. ANSTRUTHER LAWSON ON 



posed of extremely delicate threads that could be followed for short distances ; but as 

 they appear to interlace and anastomose with one another, it was impossible to determine 

 their length or their structure. In the next stages, figs. 2, 3, and 4, where the first 

 indication of the distension of the nuclear membrane was noted, we find the chromatin 

 threads slightly thicker and evidently granular and the interstices between them larger 

 and more clear. This would suggest a shortening and thickening of the threads, but 

 not a contraction. These changes continue as indicated in figs. 5, 6, 7, and 8, and they 

 appear to progress with the growth of the nuclear cavity. In these figures a very 

 interesting and important fact is revealed — namely, that the chromatin threads are 

 undoubtedly double. If these stages were examined individually, one might interpret 

 this as a longitudinal splitting of the thread at this early period ; but, by tracing the 

 series back to fig. 1, I was unable to pick out a stage where there was not evidence of 

 the double nature. This series would certainly suggest that the chromatin threads were 

 double from the beginning, but the double nature is only revealed with certainty after 

 the stages represented in figs. 5, 6, and 7 have been reached. In figs. 9 and 10 we find 

 the chromatin threads have become very sharply defined and may be followed for 

 considerable distances. Not only is the double nature of the threads more easily made 

 out, but the ends of the threads could be seen. Some of these ends are, no doubt, due 

 to sectioning, and as such appear on the surface. Many of them, however, were 

 undoubtedly within the interior of the mass, and these I take to be the actual ends of 

 the chromatin threads. As many of these ends were found — the double nature of 

 which could be made out, — this fact would indicate that the developing spireme was not 

 composed of a single continuous thread, but of a number of double threads. In tracing 

 the series back, I could not determine when the ends first became visible in the earlier 

 stages ; the threads being so delicate, one could not say positively whether one was 

 examining the granules on the reticulum or the thread ends. The inference I draw, 

 however, from these observations is that the reticulum, represented in fig. 1, is made up 

 of a definite number of threads which are double, and that this number corresponds to 

 the diploid number of chromosomes which become differentiated later. 



In figs. 11, 12, 13, and 14 we have a much better opportunity of studying the 

 double nature of the threads, for we now find them projecting out at intervals from 

 the main mass into the large clear space occupied by the nuclear sap or karyolymph. 

 In fig. 11 we see the beginning of a general loosening and separation of the threads 

 from one another. This loosening of the spireme seems to be a gradual, but irregular, 

 process. As indicated in figs. 10, 11, and 14, the ends of the threads project for 

 a short distance into the main body of karyolymph, but, as may be seen in figs. 12, 

 13. 15, 16, and 17, they soon extend out for a great length — some of them reaching 

 the nuclear membrane at the opposite side. In such cases the double nature of the 

 threads may be observed without difficulty. 



During this process of loosening and spreading out of the chromatin into the clear 

 area of the nuclear cavity the threads have continued their process of shortening and 



