Bigelow. — Nuclear Cycle of Gonionemua murbachii. 



PLATE 2. 



All figures are magnified 2600 diameters. 



Figs. 12-14. From sections. 

 Figs. 15-31. From isolated cells. 



Fig. 12. Anaphase of endodermal cell. Stout, granular interzonal filaments con- 

 nect the two chromosome groups. The centrosomes have disappeared. 



The chromosomes are closely compacted. 

 Fig. 13. Telophase. The chromosomes have become connected into an irregular 



network, and the nuclear membrane has re-formed. 

 Fig. 14. The earliest stage of the reconstruction when the nucleolus can be 



detected. 

 Fig. 15. "Resting" stage of spermatogonium. The nucleolus is compound. The 



cytoplasm contains metaplasmic masses. 

 Figs. 16, 18. Spermatogonia. The cytoplasm contains granules, which may be 



centrosomes. 

 Fig. 17. Spermatogonium with two nucleoli. 

 Fig. 19. Early prophase of spermatogonium. The nucleolar shell has begun to 



break down. There is a granule surrounded by a clear area lying on 



the cytoplasm close to the nuclear membrane. 

 Figs. 20-22. Stages in the disintegration of the nucleolar shell, and formation of 



chromatin segments by the condensation of the karyosomes. 

 Figs. 23, 24. Formation of chromomeres. The plasmatic portion of the nucle- 

 olus persists. At X one segment persists. 

 Fig. 25. A crushed cell showing various stages in the formation of chromomeres. 



There is one dumb-bell-shaped chromosome fully formed. The plas- 



mosome persists. At X one chromosome is formed. 

 Fig. 26. Late prophase. The nuclear membrane has broken down. There are 



forty-eight chromomeres connected by linin strands. The plasmosome 



has disappeared. 

 Fig. 27. Still later stage, showing the formation of chromosomes by the pairing 



of the chromomeres. 

 Figs. 28, 29. Polar views of the metaphase. Many of the chromosomes have 



split so that many more than twenty-four are visible. 

 Fig. 30. Metaphase of spermatogonium, polar view. Many of the chromosomes 



are in the process of splitting. 

 Fig. 31. Side view of spindle. The chromosomes have begun individually their 

 migration. The centrosomes are minute granules at the poles of the 

 spindle. 



