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Abstract Mitochondria of rat sperm tail middle‐piece remain associated with the flagellum after penetration of the egg by the spermatozoon and during the time of the first cleavage. During two‐ to four‐cell stages the middle‐piece mitochondria gradually swell while they separate in large clusters from the axial filament. The swelling of the male mitochondrial elements becomes more extreme during the cleavage divisions, and they finally seem to disintegrate. Thus all mitochondria found in the developing rat embryo may originate from the egg.
Dániel Szöllősi (1965) studied this question.