Ultrastructure of spermatozoa and testis of Pholcus phalangioides. (a): Early spermatid. The nucleus is surrounded by a manchette of microtubules with a peculiar regular pattern. The nuclear envelope possesses a wave-like outline. The cytoplasm in front of the acrosomal vacuole at the anterior pole of the nucleus is indented. Note the annulate lamellae near the nucleus. (b): Late spermatids. The chromatin of the nucleus is almost completely condensed. The nucleus possesses a very elongated shape with a conspicuous helical band whirling around it (arrows). (c): Detail of the nucleus. The helical band of the nucleus is very thin and bordered by microtubules (arrows). Between the band, the dense manchette of microtubules is conspicuous (arrowheads). (d): Scanning electron micrograph of a late spermatid. Note the extensive cytoplasm drop at the posterior end of the spermatid. The helical character of the nucleus is clearly visible. (e): Lumen of the testis with coiled spermatids. The coiling occurs at the end of spermiogenesis within the testis. Between the coiled spermatids several secretion droplets are visible. (f): The somatic cells possess many different vesicles and are bordered apically by microvilli. They continuously produce the large secretion droplets (arrows). AF, acrosomal filament; AV, acrosomal vacuole; Ax, axoneme; Cd, cytoplasm droplet; Fl, flagellum; Lu, lumen; Mi, mitochondria; Mv, microvilli; N, nucleus; peN, postcentriolar elongation of the nucleus; SC, somatic cell; Sec, secretion droplet; Sp, spermatids.