Spermatozoon of Pleurogenes claviger, posterior or nuclear part (Region III); all cross-sections. (a–c) Consecutive sections of the nuclear or posterior area of the sperm cell showing the appearance of the nucleus (N) and its progressively increasing size. CM, cortical microtubules; G, granules of glycogen; M2, second mitochondrion. (d) Absence of cortical microtubules. M2, second mitochondrion; N, nucleus. (e) Level of the disorganization of the first axoneme into doublets (D) and singlets (S). G, granules of glycogen; M2, second mitochondrion; N, nucleus. (f) Disappearance of the second mitochondrion and the reduction of the nucleus’ section (N). (g, h) Posterior spermatozoon extremity with and without granules of glycogen (G). Scales in μm: 0.3.