Extrusion of a Nucleolus in toto, Found in the Ovarian Oocytes of Holothuria monacaria

抄録

1. Remarkable cases of the extrusion of a nucleolus in toto from the germinal vesicle into the cytosome of ovarian primary oocytes of Holothuria monacaria were studied cytologically, and all stages of the process were traced.
2. Primary oocyte of this species has one chromatin nucleolus, which grows as large as about 7.5 microns in diameter, becomes vacuolized and finally is extruded from the germinal vesicle when it has attained a size of about 35.5 microns in diameter. A newly formed young nucleolus is found growing in the germinal vesicle when an old one is extruded.
3. The extrusion of a nucleolus takes place successively several times in the growing oocytes.
4. The nucleolus that is about to be discharged contains several vacuoles, and comes to lie close to the membrane of the germinal vesicle which now becomes slightly shriveled.
5. That part of the membrane where an extruding nucleolus attaches comes to be dented outward, and then becomes a pocket containing the nucleolus, protruding into the cytosome.
6. After the pocket containing the nucleolus has been protruded enough into the cytosome, a new membrane is formed covering the mouth of the pocket.
7. Vacuolization of the nucleolus becomes more pronounced after it has been discharged into the cytosome, and then it becomes a large, amorphous mass which stains with acidic dyes.