Some Observations on the Structure of the Peristomial Membranelle of Spirostomum ambiguum

SYNOPSIS. Electron‐microscopic observations of Spirostomum ambiguum have demonstrated additional details of superficial and deep tubular connections with peristomial and somatic kinetosomes. The superficial peristomial tubules appear to connect adjacent rows of kinetosomes. Anatomically, they course distally from the proximal kinetosomal plate. The deep tubules run proximally from the kinetosomal plate. Those in the somatic region appear to enter the endoplasm; those in the peristomial region leave the kinetosome as bundles of either 10 or 11 tubules which steadily converge to form 2 compact rows of 10 tubular bundles. These tubules connect to 2 of the 3 rows of 10 cilia each, the rows of 3 being separated by membranous folds protruding perpendicular to the peristomial groove. The rows of bundles converge further, enter the endoplasm and fan out again into tubular sheets, some of which appear to course in an antero‐posterior direction. Another set of tubules arises from each of the kinetosomes in the 3rd row of 10 kinetosomes and courses proximally at a different angle from those arising from the 2 other kinetosome rows. Terminations have not been observed for the deep somatic or peristomial tubules. Their possible role in producing the forceful longitudinal contraction of Spirostomum is discussed.