Relation between Nucleolus and Chromosomes. ia 
Very evident is the fact that the nucleolus undergoes dissolution. The 
first stage of this dissolution is a fragmentation into larger and smaller 
masses (figs. 46, 47, 48, 53, 58). Less evident is the ultimate fate of the 
nucleolar fragments. Even before the rupture of the nuclear wall the 
initial stages of the nucleolar dissolution begin (figs. 43, 50). It is usually 
consummated by the time that the first polar spindle has revolved into the 
radial position, all traces of either the plastin or chromatin elements of the 
nucleolus having been lost. Occasionally, however, a small chromatic 
nucleolus, “ metanucleus,” persists for a considerably longer time, even until 
the first polar body is formed (figs. 55, 60, 61, 62). It is ultimately also 
resorbed by the cytoplasm of the egg and is never seen until the first seg- 
mentation, when it is passed to one of the blastomeres, as described by 
Wheeler (1895) for Myzostoma glabrum (here persisting to 8-cell stage). 
The dissolution of the nuclear wall and the fragmentation of the nucleo- 
lus are synchronous processes. Undoubtedly both these processes contribute 
to the decided change that the nuclear reticulum now undergoes. Imme- 
diately prior to maturation the nuclear reticulum was achromatic and wide- 
meshed (figs. 32, 35, 38). By the time the nuclear wall has partially 
disappeared the network becomes markedly close-meshed and chromatic (figs. 
51, 52, 53, 54,55). The meshwork takes on a characteristic beaded structure. 
Such nuclear residuum (always closer meshed and deeper staining in iron 
hematoxylin than the surrounding cytoplasm) is clearly seen to persist until 
the time the first polar body is fully formed (figs. 52, 63). It accom- 
panies the polar spindle in its progress to the periphery of the egg. The 
major mass lies about the central pole, closely surrounding it and forming a 
mantle about the spindle to about the middle, and parts of it are seen even as 
far peripheralward as the distal pole of the spindle (fig. 67). Conklin 
(1905) in Cynthia and Ciona, and Lillie (1906) in Chetopterus, have de- 
scribed this “ residual substance ”’ of the nucleus in detail and have succeeded 
in tracing it through the early ontogenetic stages following fertilization. I 
was unable satisfactorily to trace the “residual substance” in the eggs of 
Asterias forbesti beyond the stage when the second polar spindle was being 
formed (figs. 70, 71). It appears that at this stage it becomes assimilated 
with the cytoplasm, probably contributing thereto the chromatin that it re- 
ceived from the nucleolus at the time of its dissolution and so playing the 
role of a “ formative stuff.” 
The nucleolar fragmentation and dissolution may occur in several dif- 
ferent ways. Usually the nucleolus breaks up into several larger masses and 
from these the chromatin gradually escapes in the shape of granules (viscid 
drops) leaving the several large masses of plastin ground-substance (figs. 50, 
52, 53, 54). Sometimes all the chromatin leaves the plastin nucleolus in a 
mass (fig. 38) and subsequently breaks up in the nucleus, the plastin being 
gradually resorbed by the protoplasm. Sometimes the plastin ground-sub- 
