Fine Structure of Platyhelminth Sperm Tails

Abstract

ELECTRON optical studies made during the late fifties led to a general acceptance of the 9 + 2 pattern in the axial filaments of cilia, flagella and sperm tails. In 1961 an exception to the universally accepted pattern was reported in the sperm tail of the trematode Haematoloechus medioplexus¹ The tail was found to contain one rather than two fibrils in the central unit, giving a 9 + 1 rather than the 9 + 2 pattern. Subsequently (1962), while commenting on the evolutionary stability of the 9 + 2 pattern, one author noted that “even the Haematoloechus observation can be explained as an unusual reaction of the central pair (and sheath) to the fixation procedure”². Also in 1962, Klima³ identified the 9 + 1 pattern in the sperm tail of the turbellarian Dendrocoelum and the 9 + 2 arrangement in the cilia of the flame cells—the first record of the two patterns in the same organism. In 1964 Silveira and Porter⁴ reported the 9 + 1 pattern in the sperm tails of three other turbellarian species, Dugesia trigina, Bdelloura candida and B. propinqua, but they found the 9 + 2 pattern in the cilia. In 1966 four additional trematode species—Gorgodera amplicava, Cotylophoran cotylophorum, Alaria arisaemoides and A. mustelae—were reported with 9 + 1 sperm tails⁵.