In order to clarify the pattern of oocyte growth in relation to follicular development in the Japanese Black cattle, oocyte and follicle diameters were compared. The relations between sizes of the oocyte nucleus and follicle and between oocyte and its nucleus were also examined. As in other mammals, the growth of the oocyte relative to that of the follicle was divided into two phases. During the first phase the oocyte grew rapidly until almost adult size, while the follicle increased only

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... in size. During the second phase the follicle grew rapidly in size, whereas the size of oocyte which had nearly reached the maximum increased only slightly. If y= phase. The value (0.1786) of b in the regression line for the first phase was within the range of the values recorded in other mammals and was similar to those obtained in other farm animals. A similar biphasic relationship was found to exist between sizes of the oocyte nucleus and follicle and between oocyte and its nucleus. Jpn. J. Zootech. Sci., 57 (3) : [244][245][246][247][248][249] 1986