Electron Microscopy of the Ectoplasm and Infraciliature of Spirostomum ambiguum

Abstract

SYNOPSIS. A study of the ectoplasm and infraciliature of Spirostomum ambiguum has been made with light and electron microscopy. Proceeding from the exterior, the cortex is described as the highly structured ectoplasmic portion of Spirostomum consisting of ectoplasmic ridge components and ectoplasmic furrow components. The pellicle invests the ectoplasmic ridges, ectoplasmic furrows, cilia, and adoral membranelles. Electron micrographs show that the cell surface is bounded by two membranes, for the most part parallel. The outer one is continuous with the unit membrane of each cilium; the course of the inner membrane has not been determined in areas bearing cilia. The ridge components are: (i) a collection of fibrils called peripheral ectomyonemes, situated beneath the inner membrane of the cell surface, oriented parallel with the organism's longitudinal axis and following the peripheral contours of each ridge; (ii) distinct rows of tubular fibrils which form a longitudinal bundle called lateral ectomyonemes, situated in the lower portion of each ridge and oriented parallel to its spiral course; (iii) cytoplasmic matrix suspending and surrounding components (i) and (ii). Mitochondria and unidentified electron‐opaque oval‐shaped or round bodies called X‐bodies are dispersed in the ectoplasmic ridges but they also occur in the endoplasm; therefore, they are considered to be transient inclusions instead of constituents of the ridges. The furrow components are: (i) the body cilia and adoral membranelles; (ii) the kinetosomes; (iii) root fibrils, called kinetodesmal strands, of the adoral membranelles; (iv) cytoplasmic matrix suspending and surrounding the furrow components. A trabecular band of randomly oriented filaments, called the endomyoneme is described as possibly the structure called M‐band by Randall and Jackson, 1958, and contractile fibrillar system by Yagiu and Shigenaka, 1963. It is suggested that collections of distinct fibrils in Spirostomum be called fibrillar complexes. Acceptance of this suggestion will lead to the designation of four distinct fibrillar complexes in heterotrichs; all four complexes have been described or mentioned in previous studies. Some findings of previous investigators are discussed and confirmed (especially pertaining to Randall and Jackson, also Yagiu and Shigenaka, cited above). Inferences from these independently derived findings are discussed.

Osmium tetroxide vapor fixation of dividing and regenerating Blepharisma

“…A trabecular band of fibers similar in both morphology and location to that just described has been observed in Spirostomum (Yagiu and Shigenaka, 1963;Finley et ^., 1964).…”

“…In Stentor polymorphus, Randall and Jackson (1958) Yagiu and Shigenaka (1963) and Finley, Brown, and Daniel (1964) have reported almost parallel observations on the ectoplasm of Spirostomum The observations of Roth (1957), Shigenaka (1964), Beams andAnderson (1961), and Pitelka (1961), dealing with protozoan fibrillar systems are also of value in interpreting the present work. Reviews by Fawcett (1961), Sleigh (1962), Pitelka (1963), andGrimstone (1961) provide excellent sources for comparison of ciliate fibrillar systems and have been used extensively.…”

“…The fine structure, particularly of the infraciliature, of other heterotrichs has been studied in more detail; similarity is apparent in those examined (Finley et^., 1964). In Stentor polymorphus, Randall and Jackson (1958) Yagiu and Shigenaka (1963) and Finley, Brown, and Daniel (1964) have reported almost parallel observations on the ectoplasm of Spirostomum The observations of Roth (1957), Shigenaka (1964), Beams andAnderson (1961), and Pitelka (1961), dealing with protozoan fibrillar systems are also of value in interpreting the present work.…”

“…No connection is observed between the filaments nearest to the right side of the ectoplasmic ridge and the inner membrane of the pellicle complex as has been reported for Spirostomum (Yagiu and Shigenaka, 1963;Finley et al, 1964); there is, however, less space separating the sub-pellicular filaments in this region (Fig. 18).…”

“…A similar system is described for the flagellate Peranema (Roth, 1959) and for Spirostomum (Yagiu and Shigenaka, 1963;Finley, ^ al•, 1964) but has not been found in the heterotrichs Gondylostoma or Stentor. Roth identifies the complex as the "subpellicular filament system" and suggests that it may be involved in the slow, contractile movements of Peranema.…”