Sperm tend to swim close to the channel walls, whereas some, but a lesser number, are swimming progressively forward along channel centerline. These progressively motile sperm cover the distance until they reach the junction channel.
Maria Portia B. Nagata, Kenji Endo, Kazuko Ogata, Kenichi Yamanaka, Junki Egashira, Naoto Katafuchi, Tadayuki Yamanouchi, Hideo Matsuda, Yuki Goto, Miki Sakatani, Takuo Hojo, Hirofumi Nishizono, Kenji Yotsushima, Naoki Takenouchi, Yutaka Hashiyada, and Kenichi Yamashita
PNAS. 2018. 115:E3087-E3096 DOI: 10.1073/pnas.1717974115