Relation between Nucleolus and Chromosomes. 71 



FIG. 54. Entire nucleolar mass has moved toward asters, leaving a vacuole and chro- 

 matin particles behind. Chromosomes are being detached from nucleolus 

 at upper border, and chromatin drops are passing out at lower border. 

 X 1320. 



FIG. 55. Chromosomes are entering the polar spindle. Nucleolus is fragmenting. 

 " Metanucleus " persisting at left. Nuclear network is becoming close- 

 meshed and chromatic. X 1320. 



FIG. 56. Oocyte in which chief nucleolus has given rise to many accessory nucleoli. 

 These left chief nucleolus as drops (witness spherical form) and evi- 

 dently manufactured their own ground-substance, from which the chro- 

 matin has in some cases become subsequently extracted. X 44- 



FIG. 57. Cross-section of first maturation spindle near one of the poles, showing the 

 chromosomes in process of transit into spindle (note size differences) and 

 fragments of nucleolus. At right several chromosomes (?) arranged in 

 manner of thread. These have not yet attained full size and final form. 

 X 2100. 



FIG. 58. One of the asters of the first polar spindle is shown. Its rays are directed 

 upon the fragmenting nucleolus. Several chromosomes and plastin 

 remnants are clearly distinguishable. X 1320. 



FIG. 59. First polar spindle is forming. Chromosomes are detaching themselves from 

 the irregular nucleolus. Nuclear membrane has entirely disappeared. 

 Extent of residual substance indicated by dotted line. X 1320. 



FIG. 60. Sectional view of median plane of first polar spindle. Chromosomes are in 

 position on the spindle fibers. " Metanucleus " with outer chromatic ring 

 persists in the residual substance of the nucleus. X 7OO- 



PLATE 5. 



FIG. 61. Oblique transverse section of spindle, showing the chromosomes in process 

 of transit into the spindle by means of the astral rays. " Metanucleus " 

 persists in the residual substance of the nucleus. X 1320. 



FIG. 62. Chromosomes are being drawn into the spindle by means of the astral rays, 

 to which they become attached. Two spherical chromatin masses ("meta- 

 nuclei"), each in a vacuole, persist in the close-meshed, beaded chromatic 

 residual substance. X 1320. 



FIG. 63. Longitudinal section of first maturation spindle, showing the chromosomes 

 entering the spindle (several have already become attached to the spindle 

 and begun the first division), a plastin remnant, the residue of the frag- 

 menting nucleolus, and the extent of the residual substance. X 1320. 



FIG. 64. Median longitudinal section of the first maturation spindle tangential to 

 surface of egg and in prophase. Centrosomes here very distinct and 

 surrounded by finely alveolar centrpspheres. Chromosomes not yet fully 

 in spindle show beginning of longitudinal fission. X 2100. 



FIG. 65. Tangential section of first polar spindle. Chromosomes not yet all on spindle ; 

 their bivalvent and bilobed character is plainly shown. The V-figures 

 show the beginning of the first longitudinal fission. X 2100. 



FIG. 66. First polar spindle with two centrosomes in central centrosphere. Rays of 

 distal aster begin to disappear. Chromosomes in metaphase. One chro- 

 mosome seen en face shows beginning of second longitudinal fission. 

 X 2100. 



FIG. 67. First polar spindle in early anaphase. Chromosomes mostly dumb-bell-shaped. 

 To the right is a large undivided chromosome. X 2100. 



FIGS. 68, 69. Two consecutive longitudinal sections of first polar spindle in anaphase. 

 Spindle has become blunt and barrel-shaped. 68 shows at the right a 

 figure representing the consummation of the first longitudinal fission giving 

 rise to four globes in serial arrangement. Above and below this are pairs 

 of smaller bilobed chromosomes representing the completion of the second 

 longitudinal fission, preparatory to the second polar mitosis. In 69 the 

 chromosomes for the most part are stubby or globular masses of chro- 

 matin. In the combined sections 20 chromosomes may be counted at each 

 pole, representing, however, probably only 18 first maturation products. 

 X 2100. 



FIG. 70. First polar body completed. Second polar spindle is being formed, its distal 

 pole arising in the region of the mid-body. Residual substance of nucleus 

 still persists. Several of the chromosomes appear to be double (the result 

 of a premature second longitudinal fission in the anaphase of the first 

 mitosis). X 2100. 



