Fig. 45. High power TEM of the cytoplasmic organization in a blastomere in a stage 2, 4-cell embryo in vitro 44 hours post-insemination (original magnification x11,900). The cytoplasm contains the organelles found in the oocyte except cortical granules are absent. The distribution of the organelles is similar to that of a 2-cell embryo. Mitochondria (M), Golgi complexes (G), and vesicular smooth endoplasmic reticulum (S) exhibit random arrangement. A few primary lysosomes (L) are also present in the cytoplasm. Mitochondria are spherical and vary in size. Some elements of the smooth endoplasmic reticulum are translucent while others are associated with mitochondria. Golgi complexes are made up of stacks of cisternae, clear vesicles, and vacuoles arising from swollen cisternae.
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