No morphological alteration appeared except in the ovary after two months in the International Space Station.

H&E staining of tissues in the ground control (GC) and spaceflight (SF) groups. Histology is shown of the caudal part of the intestine, and the liver, ovary, and testis. Scale bars = 100, 200, 50, and 50 μm for images of the intestine, liver, ovary, and testis, respectively. Arrowheads show the previtellogenic stage oocytes. Ga: cyst of type A spermatogonia, Gb: cyst of type B spermatogonia, Sc: cyst of spermatocyte, Sp: sperm mass, St: cyst of spermatocyte