Complex sentence: The subcommissural organ secretes SCO-spondin, which forms Reissner's fiber within the CSF that assist movement through the cerebral aqueduct, is present in early intrauterine life but disappears during early development.
Split into simpler sentences: The subcommissural organ secretes SCO-spondin, which forms Reissner's fiber within the CSF that assist movement through the cerebral aqueduct. It is present in early intrauterine life but disappears during early development.