THE ULTRASTRUCTURE OF THE NUCLEUS OF
THE DEVELOPING AMPHIBIAN EGG
1
SAUL WISCHNITZER
Electron Microscope Laboratory, Department of Biology,
Yeshiva University, New York, New York
I. Introduction
173
II. Nuclear Envelope
173
III. Nuclear Development
179
IV. Lampbrush Chromosomes
181
V. Nucleoli
186
VI. Discussion
189
VII. Summary
196
References
196
I. Introduction
In studying the problem of structural and genetic continuity of chromosomes, amphibian eggs were found to be especially suitable because
of the large size of their nuclear structures. This advantage exists, in
spite of the fact that the amphibian egg is not as large as that of other
vertebrate forms.
Following a 40-year period of relative inactivity, there has been, since
1950, a renewal of interest in the morphology of the amphibian egg.
This has been brought about by the development of suitable methods
permitting studies to be carried out by means of phase-contrast and
electron microscopy. This has resulted in a significant increase in our
understanding of both the morphology and physiology of the nuclear
constituents.
II. Nuclear Envelope
The nuclear envelope of oocytes is characterized by its irregular contour which can be seen with both the light and electron microscopes.
While such irregularity may be due to preparation, this feature may
1 This study was supported by a Public Health Service research grant (GM
12706-02) from the National Institute of General Medical Sciences and a research
career program award (7-K3-HD-5356-05) from the National Institute of Child
Health and Human Development.
173