ROBERTSON: THE CHROMOSOME COMPLEX. 293 



SYRBfl.A .VnMH!ARII,lS. 



are not heterochromosomes, or chromosomes of any kind, but 

 are nucleoli which for a time seem to act like chromatin bodies 

 but which later are found to be plasmosomes or true nucleoli 

 that, on account of their great density, continue to hold the 

 safranin stain for some time. Now after the last spermato- 

 gonial division where do these nucleoli go? May it not be pos- 

 sible that they still persist for a while as in figure 10? It seems 

 quite probable that the nucleoli (what Montgomery terms het- 

 erochromosomes) of his figure 13 are the same as those of my 

 figure 10, and that his heterochromosome as it lies in the region 

 of the periphery of the nucleus may have been overlooked, for 

 after the last spermatogonia! division it is often difficult to 

 distinguish it from the ordinary chromosomes, since they all 

 seem to be in a more or less semifluid and also semireticular 

 condition, much like the accessory itself. 



In Montgomery's figures following (15, 16, 17, 18, 19, 20) 

 his accessory is shown in its characteristic position near the 

 nuclear wall. He is probably correct in thinking that it shows 

 longitudinal splitting but wrong in maintaining that it shows 

 transverse constriction. In admirahilis it has shown at no 

 time a transverse constriction, nor was the longitudinal split- 

 ting noticed until the anaphase of the first spermatocyte di- 

 vision. That, however, does not prove that the splitting may 

 not be present in the groM^th period. The bent accessories of 

 his figures 18, 20, 24, 26 and 30 are not evidence of the bi- 

 valency of this element, for it often bends or coils upon itself, 

 as shown by my figures 23-28, and the bend may occur in any 

 region, not in the middle alone, and seems to be due to the 

 extreme length. During its spireme stage it passes through 

 a variety of shapes. At first it is much convoluted. Then as 

 it shortens and thickens it usually lies bent upon itself for a 

 time, but finally it becomes an almost straight rod. 



Montgomery's Y chromosome of figure 33, which w^as tardy 

 in coming to the equator but which he claimed did so later on, 

 although he gave us no assurance of it in his drawings, is in 

 all probability the accessory chromosome, for it agrees with 

 what we have found for admirahilis, where in every cell at 

 this stage it may be seen starting off undivided ahead of its fel- 

 lows to one of the poles. Montgomery was wrong, however, 

 in supposing that it had not yet taken up its position in the 

 equator. In fact, it has already been there, as the dividing of 



