58 embryos at 1, 2, 3 and 4 cell and morula stage were recovered from the oviduct and the uterine horn of the Ha-bai, Du-ha and Du-chang-ha pigs, 24 hours, 2 or 3 days of pregnancy, and were observed with SEM and TEM. The zona pellucida of 1 cell embryo was removed by treatment with 2.5％ pronase for visualization of the cell surface structure.The findings are as follows:1. The surface of the 1 cell stage embryo was densely populated with microvilli and sperm can be found on the surface with its head and tail surrounded by the microvilli and its plasma membrane of the equatorial segment of acrosome intact.2. Many spermatozoa were observed both on the surface and inside the zona pellucida of the 2 celled embryo.3. By the 4 cell stage, some of the spermatozoa had penetrated through the zona and got into the perivitelline space. 4. There were still some spermatozoa on the zona surface of the morula.5. The TEM observation revealed that the heads of supernumerary sperm were located within the cytoplasm of the blastomeres of the embryos from 1 to 4 cell stages and still not decondensed. Some of these sperm heads were actually found within the phagocytic vacuoles of the 4 celled embryos. The ultrastructure of these polyspermic embryos was normal.These results showed that polyspermy in the pig did not intefere with the cleavage of the embryo and the embryo possessed the ability to dispose the excessive sperms.

On 10 days of pregnancy the blastocysts of 3 mm and 9 mm in diameters wereflushed out from the uterine horns of the Du-Chang-Ha and Dong-Bei-Min pigs.The blastocysts were divided into four parts,that is the embryonic disc,the animalpole,the lateral part and the vegetal pole.The outer and inner surface of the fourparts were observed with SEM and the findings are as follows:1,The 3 mm blastocystsThe outer surface of the embryonic disc was still covered with trophoblasticcells.Three kinds of cells can be discerned:the cell with round prominences andlong microvilli(MV);the cell with thin and long MV,the cell with smooth sur-face.The trophoblast cells in other areas of the blastocyst were similar but slightlyflat.The inner surface of the blactocyst consists of endoderm cells which weredifferent in the four parts.From the embryonic disc to the vegetal pole,the surfacestructure of the endoderm cells changed regularly from small to large from dome-shaped to flat and the distance between nuclei increased gradually.The MVs on thecell surface:became less.These findings suggested that endoderm cells weremoving from the center of the embryonic disc to the vegetal pole.There weremany holes on the marginal area of the cells.The edge of the cell on the innersurface of the vegetal pole forms a network.Many round granules can be seen inthe holes of the network.Their function may be for the transport of nutrients.2,The 9 mm blastocystsThe outer surface of the embryonic disc was not covered with trophobla-stic cells but covered with ectoderm cells.The ectoderm cells in the primitivestreak had long MV on their surface but short ones on other areas of the disc.The inner surface of the embryonic disc was endoderm cells.The MVs on theendoderm cells was much more numerous than the MVs on the ectoderm cells.Thedifferentiation of the cells in the pig blastocyst was also discussed.

Light and electron microscopic observations revealed that most of the embryos collected 15-16 hours after fertilization were at the pronuclear stage. Many supernumerary spermatozoa were found on the surface and in the outer zone of the zona pellucida, but none of them got into the inner zone of the zona or the perivitelline space. Some spermatozoa on the zona surface were observed in acrosome reaction stage, and those penetrated into the zona always left some acrosome reaction vesicles behind on the surface of the zona. The fertilized ovum eliminated almost all of its cortical granules and where there were some granules left, in the area that the plasma membrane had fewer microvilli. The cortical cytoplasm of the pronuclear zygote was populated with clustered hooded mitochondria, SER vesicles, yolk vacuoles and lipid droplets. Directly surrounding the pronucleus were a variety of organelles including welldeveloped Golgi complex, SER, mitochondria and annulate lamellae. The significance of these morphological changes of the fertilized ovum was discussed.

The cytoplasmic and nuclear changes during the development of goat oocytes were studied with light and electron microscopy. The oocyte development may be divided into 8 stages in accordance with the number and distribution of follicle cells and the size of the follicle. The results indicated that the Golgi complex, mitochondria, smooth endoplasmic reticulum and cortical granules became well developed and they moved into the cortical region as the oocyte development proceeded. In the oocytes in the follicle of 1.5-3mm in diameter, all the mitochondria became hooded and the number and size of fibrillar centers in the nucleolus reached maximum, but the nucleolar compaction still not occured at this stage. By the time when the follicle reached 3.5-5mm in diameter, the follicular cell processes began to degenerate, the microvilli of the oocyte withdrew from the zona pellueida and the oocytes might be cultured to mature in vitro. In the mature oocytes, Golgi complex and rough endoplasmic reticulum disappeared, the cortical granules arranged themselves in one layer beneath the oolemma, the mitochondria dispersed in the central region of cytoplasm and the eggs were ready for fertilization.