1. The ovaries of the mouse were ultra-centrifuged at a force of about 130,000 times gravity.

2. The young oocyte is stratified into three layers: lightly stained cytoplasm, usually containing a few small granular Golgi elements, in the centripetal end of the cell; a middle layer of Golgi elements containing the nucleus; a centrifugal layer of mitochondria.

3. In the larger oocytes a thin layer of yolk is present between the Golgi layer and the centripetal pole, while a layer of nongranular substance is present at the centrifugal pole.

4. The mature oocyte is stratified into four layers: a lightly stained centripetal layer; a layer of yolk; the Golgi layer; a centrifugal layer of mitochondria. The Golgi layer is now divided into two parts; the centrifugal part contains numerous mitochondria amongst the Golgi elements.

5. The nucleolar material is the heaviest substance in the nucleus; it increases in density with the growth of the egg. In the mature oocyte the nucleus lies in the mitochondrial layer; the nucleus is thrown towards the centrifugal pole by the weight of the nucleolus.

6. The Golgi elements are in the form of granules, rods, and of irregularly shaped bodies. It is probable that the localized Golgi material of the mouse egg is not in the form of a network.

7. Fat was not identified in the normal ovarian eggs, but is present in degenerating ova. The Golgi elements give rise to the fat of degenerating eggs.

8. The inclusions and components of the follicle-cells were not always affected by the force necessary to bring about stratification of the oocyte. The degenerating eggs were not stratified.

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