Various cell components such as yolk nucleus, loose basophilic substance, mitochondria and lipid bodies (L2) proliferate with the growth of previtellogenic oocytes in cat and dog, investigated with various histochemical techniques. The yolk nucleus and its fragments consist of RNA, protein and some lipoprotein. The loose basophilic substance reacts mainly for RNA and protein. The mitochondria show phospholipid and protein. The lipid bodies (L2) contain phospholipid. The sites of distribution of lipid bodies (L2) and vacuoles in the oocytes and granulosa suggest a nutrient transfer design. Some large vacuoles, which react negatively with the various techniques used, gradually accumulate in the central cytoplasm of large oocytes which abundantly store sudanophilic lipid yolk droplets of various sizes. These consist mainly of phospholipid and neutral fat (triglyceride); the latter increases in amount during atresia of oocytes. They are formed by the coalescence and condensation of small lipid granules whose precursors appear to be transported from outside the oocyte, as judged from the corresponding infiltration of lipids through the zona pellucida into the oocyte. The incoming lipids are physicochemically changed before they are converted into lipid yolk droplets. This change may be brought about by the peripheral cell organelles (mitochondria and yolk nucleus substance) and ground cytoplasm. The direct transformation of cell organelles into lipid yolk has been ruled out in the present material.
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Sardul S. Guraya (1965) studied this question.