The reformation of nuclei and cells on the basis of yolk granules in vitro has been examined under electron microscope by using the mature ooeytes of the middle female intersex of Chirocephalus nankinensis. And it has been shown that the forms of reformed nuclear and cellular structures vary, which may be related to the developmental stages of the middle female intersex, types of reforming process, culturing times as well as internal and external conditions of yolk granules. We have also studied the structural changes of yolk granules and some transition forms during the reformation of nuclei and cells. The results are fairly in agreement with those of our previous reports, i. e. the time-lapse microcinematographic and phase contrast studies on the cell reformation of yollk granules in vitro and the electron microscopic investigations on the cell reformation of yolk granules of mature oocytes in situ. The reformation of nuclei and cells on the basis of yolk granules in vitro has been examined under electron microscope by using the mature ooeytes of the middle female intersex of Chirocephalus nankinensis. And it has been shown that the forms of reformed nuclear and cellular structures vary, which may be related to the developmental stages of the middle female intersex, types of reforming process, culturing times as well as internal and external conditions of yolk granules. We have also studied the structural changes of yolk granules and some transition forms during the reformation of nuclei and cells. The results are fairly in agreement with those of our previous reports, ie the time-lapse microcinematographic and phase contrast studies on the cell reformation of yollk granules in vitro and the electron microscopic investigations on the cell reformation of yolk granules of mature oocytes in situ.