ON THE FINE-STRUCTURE OF SPERMATOZOA OF TACHYPLEUS-GIGAS (XIPHOSURA, MEROSTOMATA)

Among the Arthropoda the Xiphosura are the only group whose spermatozoa resemble the so-called ''primitive type'', although even here there are some differences. The spermatozoa of Tachypleus consist of a sperm head, a middle piece, and a long flagellum. Though principally quite similar to the spermatozoa of Limulus polyphemus some characteristics are noticeably different: the axonemal pattern (9 .times. 2 + 0), the shape of the acrosomal vacuole, the different position of the acrosomal filament, and the distribution of mitochondria throughout the cytoplasm. In contrast to what is known from Limulus the nuclear envelope is apparently dissolved over wide areas. Consequences for the interpretation of the acrosomal reaction are discussed. Structural conditions are compared with those in other Chelicerata.