Bigelow. — Nuclear Cycle of Gonionemus Murbachii. 



PLATE 4. 



All figures are from isolated cells, and are magnified 2600 diameters. 



Figs. 55, 56. Late prophase. The chromatin net has segmented into twenty- 

 four separate chromatin bodies. The nuclear contents are some- 

 what contracted. 

 Figs. 57, 58. Still later prophase. The nuclear membrane lias disappeared. The 



twenty-four chromomeres are still separate. 

 Fig. 50. The chromomeres are dense, and have commenced to pair. 

 Fig. 60. Late prophases. Eight bivalent chromosomes have been formed by the 

 pairing of the chromomeres ; six chromomeres are still separate. 

 The linin strands connecting the chromomeres still persist. 

 Fig. 61. Early metaphase, polar view. There are twelve bivalent chromosomes. 

 Figs. 62-64. Metaphase of the common type, side view. The chromosomes are 

 dumb-bell-shaped, and are divided by a pulling apart of the thick- 

 ened ends. 

 Figs. 65, 66. First maturation spindles of the rarer type. The chromosomes are 

 already divided, and have begun individually their migration 

 toward the poles. They are much larger than spermatogonial 

 chromosomes. 

 Fig. 67. Oblique view of the two daughter plates of the first maturation division, 



showing twelve large chromosomes in each. 

 Fig. 68. Anaphase of first maturation division. The chromosomes are very 

 large and closely crowded. Stout, granular, interzonal filaments 

 connect the two daughter groups. 

 Fig. 69. Telophase. The chromosomes have become connected into an irregular 



network. 

 Fig. 70. Still later telophase. The reticulum is loose. The right-hand cell bears 



a rudimentary filament on its margin. 

 Fig. 71. A pair of secondary spermatocytes. The nucleolus has re-formed, in 

 each, and consists of several granules. The interzonal bridge still 

 persists. 

 Fig. 72. " Resting " stage of secondary spermatocyte. The nucleolus is now a 



homogeneous structure. 

 Fig. 73. Prophase of secondary spermatocyte. The nucleolus has broken down, 



and the karyosomes have increased in size. 

 Figs. 74-79. Various stages in the prophase of the secondary spermatocyte show- 

 ing abnormal contraction phases. 

 Fig. 80. Prophase. Successive stages in the formation of the chromatin reticulum 



by condensation of the chromomeres. 

 Fig. 81. Still later prophase. The nuclear membrane is still intact. Twelve 



chromosomes are now formed. 

 Figs. 82, 83. Polar views of metaphase of second maturation division, showing 



twelve chromosomes. 

 Fig. 84. Metaphase of second maturation division. The centrosomes are prom- 



inent. 

 Fig. 85. Anaphase. The chromosomes are much smaller than in the first matu- 

 ration division. Stout interzonal filaments connect the daughter 

 groups. 



