24 THOS. H. MONTGOMERY jr., 



Such is the remarkable mode of transformation of a chromosome 

 into a chromatin nucleolus, a process which I believe has never been 

 noted before. So peculiar is this metamorphosis, that I was at first 

 unable to believe what a thorough study has subsequently shown to 

 be the facts. These phenomena show us the remarkable process of 

 the casting off of an entire chromosome , which is itself possibly a 

 mode of chromatin reduction; and in the two spermatocytic divisions 

 we shall find that the chromatin nucleolus does not again become a 

 chromosome. My preparations demonstrate with great clearness, and 

 not in a few but in hundreds of cells, all the stages of this formation, 

 from the first appearance of the red-staining chromosome among the 

 violet ones to its gradual rounding off as a well marked element. 

 There are only two other thinkable modes of origin of the chromatin 

 nucleolus: 1) that it be extranuclear in origin, or 2) that it be a 

 secretion of the chromatin. If it were extranuclear in point of form- 

 ation, one should find a substance in the cytoplasm staining like it, 

 and this substance close to the nuclear membrane. But the only 

 demonstrable secondary substance in the cytoplasm is the yolk, which 

 does not make its appearance until the close of the synapsis, and 

 the yolk always stains differently. Further, the chromatin nucleolus 

 lies at first within the nuclear cavity, among the chromosomes, and 

 only later comes situated close to the nuclear membrane. Again, how 

 explain its similarity in form to the chromosomes, if it were an extra- 

 nuclear product? Is it then a secretion product of the chromosomes? 

 This also cannot be the case, though at first I inclined to this as- 

 sumption. For when it is first distinguishable from the chromosomes, 

 it has the same form and shape as the latter, and for a short time 

 continues to elongate exactly as they do. Were it a secretion of 

 the chromosomes it should first appear as globules or portions of sub- 

 stance apposed to the surfaces of one or more of the chromosomes, 

 but I have looked in vain for evidence of such appearances. But it 

 is not on these negative conclusions that I base my conclusions as to 

 the chromosomal origin of the chromatin nucleolus, since I have thus 

 only endeavored to forestall possible objections to my views; my con- 

 clusion is based on the direct observation of hundreds of cells, showing 

 the continuous series of changes from the chromosome of the early 

 anaphase to the chromatin nucleolus of the resting cell. 



In the spermatocytes of Harpalus a chromatin nucleolus has 

 been seen by me, besides the true nucleolus; and judging from the 

 observations of authors on various objects it would seem that such a 



