The usual axonemal arrangement of microtubules is
1
6 pairs of doublets radially arranged at the periphery with a pair of centrally located microtubules
2
6 pairs of doublets radially arranged at the periphery with a single centrally located microtubule
3
9 pairs of doublets radially arranged at the periphery with a pair of centrally located microtubules
4
9 pairs of doublets radially arranged at the periphery with a single centrally located microtubule