Spermatozoon of Pleurogenoides medians. (a, b) longitudinal sections; all others, cross-sections. (a) Anterior spermatozoon extremity (ASE). Ax, axoneme; C, centriole. (b) Detail of the anterior spermatozoon extremity (ASE). (c, d) Consecutive sections showing the appearance of the centrioles (C1 and C2) and cortical microtubules (CM). (e–h) Consecutive sections of the anterior area of the spermatozoon showing the appearance of the first mitochondrion (M1) and the two and four attachment zones (arrowheads). Thus, parallel cortical microtubules (CM) transform from a submembranous continuous layer into two fields. (i, j) Ornamented area. Note the presence of external ornamentation of the plasma membrane (EO), spine-like bodies (SB) and the second mitochondrion (M2). M1, first mitochondrion. (k) Middle part of the sperm cell (or Region II) showing the stopping of the first mitochondrion (M1). CM, cortical microtubules; M2, second mitochondrion. (l) Anterior part of the nuclear region. CM, cortical microtubules; G, granules of glycogen; M2, second mitochondrion; N, nucleus. Scales in μm: (a, c–l), 0.3; (b), 0.1.