Ultrastructure of the vas deferens of Pholcus phalangioides. (a): The spermatozoa are embedded in a dense secretion matrix. Between the spermatozoa three kinds of secretion droplets are visible. The secretion droplet type 3 is characterized by an irregular surface which sometimes includes other particles (arrows). (b): The epithelium of the vas deferens is very flat and bears microvilli. It is basally bordered by a thin muscle layer. Note the thick secretion sheath which surrounds each spermatozoon. (c): Scanning electron micrograph of the seminal fluid. Note the irregular surface of the secretion droplet type 3 and the differences in size of spermatozoa and secretions. Lu, lumen; Mu, muscles; Mv, microvilli; Sec1–3, secretions of droplet type 1–3; Sp, spermatozoon; SSh, secretion sheath.