Miscellaneous. 161 



MISCELLANEOUS. 



Polomyxa palustris, a freshwater Amoeboid Organism. 

 By Dr. Richakd Gkeef. 



The genus which forms the subject of this memoir was briefly de- 

 scribed by the author in 1870, under the name of Pelohius ; 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 grej-ish bodies averaging 1 millim. in 

 diameter, but sometimes attaining U millims., or even more. The 

 smallest indi\-iduals 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 diff'erent 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 diff'erent 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"), 

 i^hining bodies (" Glanzkorper "), and bacilli (" feine Stabchen ''). 



The nuclei, which are alwaj-s disseminated in great quantities 

 Ann. ((• Mar/. N. Jlisf. Ser.4. To/, xiv. 11 



