Miscellaneous. 161 MISCELLANEOUS. Pelomyxa palustris, a freshwater Amoeboid Organism. By Dr. Richard Gkeef. The genus which forms the subject of this memoir was briefly de-scribed by the author in 1870, under the name of Pelobius ; but this denomination has been abandoned by him, on account of its being previously applied to a genus of Coleoptera. Pelomyxa palustris, the only known species, is found abundantly at all seasons at Bonn and Marburg ; but it is in spring and the beginning of summer that it seems especially to develop itself ; and it then covers the upper layers of the mud in great masses. It is observed in the form of little greyish bodies averaging 1 millim. in diameter, but sometimes attaining 2 millims., or even more. The smallest individuals are little points, scarcely visible with the simple lens. Under the microscope the contracted Pelomyxa usually appears spherical, ovoid, or lenticular. It is composed of protoplasm, in which two layers of different nature may be distinguished — a cortical layer, and a parenchyma. The outer layer, which appears to be pure protoplasm, is hyaline, homogeneous, and of a more viscid consistency than the parenchyma. It swells up into rounded vesicles projecting at the surface of the mass, and sometimes lobed or digitate, into which the inner surface penetrates as into a sac. These processes creep or flow by amoeboid movements, which cause the advance of the whole Pelomyxa. The inner parenchyma is of a more fluid consistency, and so closely filled with vacuoles that it appears quite reticulated. It seems only to take a passive part in the movements, and is merely carried in one direction or another as mobile contents under the action of the contractions of the outer layer. It is this inner substance that contains all the other parts, both those belonging to the organism itself and those which have penetrated from without. The very dark coloration which it often presents is due to the nature of the ingested food, which consists of animal and vegetable substances, to which a great quantity of grains of sand and fragments of mud is added. The vacuoles are of different sizes, and more or less closely packed ; and they constantly change their positions under the in-fluence of the amoeboid movements of the whole body. They are simple cavities, the perfectly clear contents of which rarely contains a few dark granules and is of a totally different nature from the enveloping substance. Dr. Greef believes that they contain nothing but water. Besides the vacuoles, there are in the inner parenchyma three sorts of distinct bodies — which Dr. Greef names nuclei ("Kerne"), shining bodies (" Glanzkorper "), and bacilli (" feine Stabchen "). The nuclei, which are always disseminated in great quantities Ann. & Mag. N. Hist, Ser. 4. Vol. xiv. 1 1
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