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Papers from the Marine Biological Laboratory at Tortugas. 
. Odcyte showing the passage of chromatin from nucleolus to adjacent chromo- 
some group just prior to maturation. > 700. 
. Nucleus in which the chromosome mass and nucleolus are at opposite poles. 
The chromosomes are in position to meet the polar spindle, which is about 
to form. The chromatin of the nucleolus is seen leaving the vacuolated 
plastin ground-substance (plasmosome) en masse and moving toward the 
chromosomes, at the same time contributing chromatin to the achromatic 
nuclear network. The peripheral layer of yolk granules is also shown. 
<3320: 
Primary odcyte at culmination of growth-period and some time prior to 
maturation. The eccentric nucleolus is homogeneous, with some of the 
chromosomes closely attached. The nuclear network is wide-meshed, 
beaded, and slightly chromatic, and with occasional karyosomes. The 
peripheral layer of the egg is filled with large yolk-granules. X 1320. 
IPPATE! 35 
_ Nucleus with chromosomes gathered into three groups (a, b, and c). These 
are enlarged at a, b, and c, X 2100. The majority of the chromosomes 
are bilobed. Their number is approximately 18. > 700. 
. Odcyte in which the chromosome mass lies very close to the nucleolus. X 440. 
. Odcyte showing the beginning of the establishment of a chromatin connec- 
tion between nucleolus and chromosome group. XX 440. 
. Odcyte in which the chromosome mass is less compact. Nucleolus is break- 
ing up and establishing connection with the chromosomes. % 700. 
. The above mass of chromosomes magnified 2100. About 15 chromosomes 
may be counted. 
. Cross-section of central pole of first maturation spindle after first polar body 
has been constricted off (this seen in next section), showing 20 chromo- 
somes, the excess of 2 chromosomes above the usual number of 18, 
due to a premature longitudinal splitting of two of the elements. Com- 
pare with figure 44. > 2I00. 
Maturing odcyte in which spindle is forming and the astral rays have pene- 
trated far into the nucleus. Both chromosome group and fragmenting 
nucleolus near distal pole of nucleus. There are no chromosomes among 
the rays in this or any of the adjacent sections. X 700. 
Oécyte in initial stages of maturation, showing the nucleolus in transit toward 
the polar spindle, leaving a vacuole (the remains of the resorbed plastin 
ground-substance) and chromatin particles behind. The chromosome 
group has already separated and some of its elements have passed among 
the astral rays. > 700. 
Composite figure of two consecutive sections. Nucleolus seen to break up 
at one pole of the nucleus, leaving a plastin remnant. Spindle forming 
at opposite pole with several chromosomes already drawn toward it. 
X 700. 
PLATE 4. 
Primary odcyte showing nucleolus and chromosomes at opposite poles of 
nucleus. Maturation is imminent and the chromosomes are in proper 
position to be drawn into the spindle soon to appear. Chromatin in 
form of beaded threads is seen to pass from nucleolus toward chromo- 
somes. XX 700. 
Two centrospheres with centrosome and aster pushing into nucleus. Nuclear 
wall still intact. Nucleolus in process of dissolution. Two chromosomes 
are seen emerging from the mass. XX 1320. 
Composite figure of three consecutive sections, showing one aster (a), a 
group of chromosomes scattering (several are detaching themselves from 
nucleolar mass of chromatin), and a spherical chromatin mass (0), and 
two additional spherical nucleolar masses (c). > 700. 
. Chromosomes are entering the polar spindle. Last one in process of being 
detached from mass of disorganizing nucleolus. Nuclear network very 
close-meshed and highly chromatic. > 1320. 
. Nuclear wall is ruptured. First polar spindle is being formed. Nucleolus 
is breaking up. Chromosomes are becoming attached to astral rays. Nu- 
clear network is becoming close-meshed and more chromatic. X 1320. 
