19c6] MERRIMAN—NUCLEAR DIVISION IN ZYGNEMA 45 
ing granules in the living cell renders the nuclei about to divide easily 
distinguishable from the remainder in the filaments. Owing to the 
activity of these granules, changes going on within the living nucleus 
could not be easily followed, but changes in the form and position 
of the nucleus together with those of the pyrenoids were followed 
throughout division. Accordingly the history of changes in the 
chromatin is all deduced from comparison of dividing nuclei stained 
by haematoxylin or safranin as outlined above. 
If haematoxylin in combination with iron alum could be considered 
as an infallible criterion for distinguishing chromatic from achro- 
matic material, and stages could be selected from material stained 
by one of the methods only, it would be an easy matter to trace the 
history of this central body originating from the chromosomes of the 
metaphase. Often, as in fig. 2b, numerous deeply stained bodies 
are to be seen lying in the space surrounded by a membrane, with 
no trace of chromatin bodies without. In the nucleus represented 
in fig. 5, in place of the central body several smaller bodies can be 
seen marked off from the eosin-stained bodies by the blackness of 
the stain. Passing to fig. 9, where the beginnings of an intranuclear 
spindle are manifest, and where there are several more deeply stained 
bodies, and then to jig. 12, where six discrete bodies distinctly form 
an equatorial plate, the natural conclusion, based wholly upon simi- 
lar staining properties, would be that the central mass of chromatin 
alone furnishes the chromosomes for the equatorial plate. Such 
was the conclusion reached during the first year of this investigation, 
but further study of the material shows it to have been premature, 
or, if applicable at all, only to a few cases. The conviction that 
_ difference in staining of nuclear structures is more often a matter of 
manipulation than of chemical reaction, and that difference in the 
shade produced by the stain is merely due to the density of the body 
and time given for penetration, renders necessary in interpretation a 
great degree of caution. 
The following account is derived from a comparison of parallel 
Stages in all the preparations. 
As the nuclei pass from the quiescent to the active state, the cen- 
trally lying mass disintegrates into small bodies (figs. 2, 3); at the 
same time the granules lying at the periphery increase in size. The 
