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Microscopy of coverslips that had been allowed to float on water from an aquarium standing over sand in a deep Petri dish revealed the presence of two kinds of colorless flagellates living in stalked, transparent vase-shaped houses (Fig. 1). One of the flagellates inhabits an urn-shaped house which in my material was invariably attached to the sheath around chains of the bacterium Sphaerotilus natans. The other flagellate builds flared cups on relatively long stalks attached directly to the substrate (Figs. 4 and 5). Collodion-coated grids for electron microscopy were placed on the surface of the water and on the following day were found to have been settled by the two flagellates, Sphaerotilus natans, and many other microorganisms. To the water in the dish was added an equal volume of 10 per cent neutral formalin and 10 minutes later the grids were removed, rinsed 3 times in large volumes of distilled water, dried in air, and without further treatment were examined in a Philips electron microscope (100-A). The houses of the fagellates were transparent and were marked by closely spaced transverse lines (Figs. 2 and 3). The urn-shaped variety was striated only in its lower half, but the flared cups bore a pattern of similar but more widely spaced transverse lines right up to the lip. At first glance the lines seem to run parallel to each other but closer inspection reveals that those marking the flared cup shown in Fig. 4 are really turns of a very shallow helix. I am indebted to Mr. Roderic Pontefract of our laboratory for pointing this out to me. From a photograph (Fig. 1) and electron micrographs submitted to him since the Arden House Meeting, Professor E. G. Pringsheim of the Pflanzenphysiologisches Institut at the University of Goettingen, Germany, has recognized the flagellates as members of the genus Bikosoeca, discussed in detail by Picken (1941) and Pringsheim (1946). The precise identity of the organism shown in Figs. 1 and 2 is in doubt, but Figs. 4 and 5 are almost certainly Bikosoeca petiolata. Pringsheim (1946) has discovered that the houses of some Bicoecidae con233

OBSERVATIONS ON VASE-SHAPED, IRON-CONTAINING HOUSES OF TWO COLORLESS FLAGELLATES OF THE FAMILY BICOECIDAE