Figure 4. The mammalian sperm central pair apparatus (CPA) has a conserved projection network but species‐specific microtubule inner proteins.

• A–C
  Whole‐population in situ structures of the 32‐nm CPA repeat from pig (A), horse (B), and mouse (C) sperm. Panels (i), (ii), (iii), and (iv) are cut‐through views of the lumens of the C1 (i and ii) and C2 (iii and iv) microtubules. Microtubules are shown in gray and microtubule protein densities are colored individually. The projection network is colored according to (Carbajal‐González et al, 2013).