The Stomach Cell of Rotifer

Some details of the uhrastructure of the syncytial stomach cell of the rotifer have been presented by Lansing (1). He has described the luminal membrane of the stomach cell as consisting of a thick reticular layer beneath a unit membrane 60 A thick. He noted a similarity between this layer and the terminal web of the intestinal epithelium. Lansing further observed goblet-shaped pockets in the gastric luminal surface. Ingested colloidal gold particles were observed in these pockets and in cytoplasmic food vacuoles which led Lansing to postulate that the gold particles entered the cell cytoplasm through the gobletlike structures. This communication will present details of a fine "crystalline" organization of a region immediately surrounding the gobleflike projection. A Philodina species was selected from a mixed rotifer culture obtained from Turtox Products General Biological Supply House, Inc. Organisms were fixed in a contracted state by 1% osmium tetroxide buffered to pH 7.5 in McEwen's saline (2). Some of these rotifers were prefixed in 6% glutaraldehyde and postfixed in osmium tetroxide. In order to fix rotifers in an extended state, some animals were "paralyzed" in 0.5% neosynephrine (3), and subsequently fixed in 2 % unbuffered osmium tetroxide. It has been somewhat more difficult to obtain details of ultrastructure with the last procedure as compared to the former methods; however, fixation in extension is desirable for orientation purposes. All fixed specimens were dehydrated in ethanol and embedded in Maraglas (4). Thin sections were cut on a Porter Blum microtome, stained with lead citrate (5), and examined in an RCA EMU-3E. Fig. 1 depicts an oblique section through the lumen of the syncytial stomach of a rotifer. The lumen of the gut contains cilia, and it is bounded by a unit membrane (Fig. 2) as described by Lansing (1). Beneath the membrane is a relatively homogeneous region which stains rather lightly. In cross-sections of the gut (Fig. 2), this region appears finely granular or amorphous, whereas in longitudinal sections (Fig. 1) it appears to consist of thin fibers approximately 30 A in diameter. In keeping with the terminology employed by Lansing (1), this area will be called the terminal web. Scattered within the terminal web are the roughly cylindrical "goblet-shaped" bodies described by Lansing (1). Their appearance is somewhat variable. Some appear to open into the stomach lumen (Fig. 1), whereas others appear separated from the lumen by one or two unit membranes (Fig. …