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 Chatoptcrus 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. 1/6). 



In Asterias forbesii 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 Chatopterus. 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 



