Relation between Nucleolus and Chromosomes. 55 
gather together more closely and often lie immediately around and upon the 
nucleolus. In some cases it looks as if these chromosomes were being 
formed out of the substance of the nucleolus . . . and though it is possible 
that they may later receive substance from the dissolving nucleolus, it is im- 
possible to suppose that they are fragments of the nucleolus.” The latter 
states in the case of Chetopterus that “the chromosomes begin to separate 
from the surface of the nucleolus as soon as the wall of the germinal vesicle 
is ruptured, and the nucleolus (in consequence?) appears shrunken and 
vacuolated ” (p. 176). 
In Asterias forbesu I found many eggs in which the relation between 
the chromosomes and nucleolus was far less intimate than that described 
above in the case of Crepidula and Chetopterus. Indeed, numerous tran- 
sition stages were found between such in which the nucleolus and chromo- 
somes were at opposite poles of the nucleus and such in which the chromo- 
some mass was closely applied to the nucleolar surface. Figures 38, 41, 
42, 43, show such transition stages. In figure 46 the fragmenting nucle- 
olus was at the pole nearest to the aster and its rays were seen really 
to touch the chromatin mass. The chromosome group was near the 
opposite pole of the nucleus. No chromosomes or chromatin masses could 
be found among the astral rays. This is additional proof that no chromo- 
some could come from the nucleolus alone. In another case, where the 
nucleolus was breaking up at the opposite pole of the nucleus, while the 
chromosome group was situated next the aster, some chromosomes were 
seen among the rays (figs. 47, 48). These could not under the circum- 
stances have come from the nucleolus. In these cases the chromosomes are 
always very small. 
Where the separation of the nucleolus and chromosome mass is of less 
distance there is very clearly evident a tendency for the two to get into more 
intimate connection. Frequently a chromatin thread is seen to pass out 
from the nucleolus (figs. 30, 31, 32, 36). Delicate threads of chromatin 
and small chromatin masses are also seen to pass from the nucleolus into the 
nuclear reticulum (figs. 35, 38, 49) to which they probably give its darker 
staining capacity, which is seen to progressively increase at this time. 
Where the distance between the nuceolus and chromosome mass just pre- 
vious to maturation is slight there is usually a chromatin cross-connection 
between the two. It appears very probable that the normal condition is a 
very close connection between nucleolus and chromosomes (figs. 37, 41). 
Perhaps if the eggs had been allowed to be shed and mature normally, a 
very close connection between nucleolus and chromosomes would in all cases 
have been established before the chromosomes were drawn into the spindle. 
It is possible that in these artificially matured eggs sufficient time had not 
been given for the two to draw together. That eggs in which such close 
connection is not attained may still mature normally is proved by many 
