[A and C particles in mouse embryos].

Electron microscopic examination of embryos of the BALB/c and AKR strains of mice from the 1-cell stage to 14 days of age revealed 2 types of intracisternal A particles, one type of C particle budding into the extracellular space and an endoplasmic reticulum-association "dense-cored veiscle". The occurrence of the particles showed a marked dependence on the developmental stage of the embryo. A small percentage of 1 blastomere embryos in both strains showed the presence of a small number of A particles. Embryos of 1 to 16 blastomeres of the AKR strain with A particles were on average more frequent than in the BALB/c strain. The percentage of 7 and 14 day embryos with C particles was much greater in AKR than in Balb/c mice.