[The effect of weightlessness on embryonic development of striated muscles in Japanese quail]

In the conditions of gravitationless state, the development of skeletal muscles and myocardium was identical in experimental, synchronous and laboratory control. There were not larger differences between the investigated groups of animals. Myofibrils were in the stage of myofibrillogenesis. They were mostly disarrayed, but they already formed sarcomeres, without marked boundaries between I and A zones. Sarcoplasm contained large amounts of ribosomes and polyribosomes. Mitochondria were intensively splitting, and they contained small numbers of mitochondrial particles. Osmiophilic bodies and granules were detected frequently. Sarcoplasmic reticulum and Golgi apparatus were well developed. Our findings are in agreement with the results published in papers dealing with the embryonal development of striated muscles.