Principal piece
This high-power picture shows the principal piece of the spermatozoon in cross section. You see clearly the 9 + 2 structure of microtubules centrally (the axoneme) and a fibrous layer externally.
This high-power picture shows the principal piece of the spermatozoon in cross section. You see clearly the 9 + 2 structure of microtubules centrally (the axoneme) and a fibrous layer externally.