AMOEBA. 185 



the naked and not shell-bearing forms of Rhizopoda have been found. 

 The latter we must, for other reasons, regard as exclusively confined 

 to water or damp earth. 



We must again, however, remember that fragments of cellular 

 tissue may be easily confounded with true Amoebae, and many so- 

 called Amoeba may be only a developmental stage of entirely different 

 animals. We know even of active Rhizopod-like fungi (the so-called 

 Myxomycetes'), which, in their youth, are exactly like Amoebce 1 (Myxa- 

 mcebce), and may, under certain circumstances, live for a long time as 

 such. 2 



Amoeba, Ehrenberg. 



Auerbach, " Ueber die Einzelligkeit der Amceben," Zeitschr. f. wiss. Zool, Bd. vii., 

 p. 365, 1855. 



Naked Ehizopoda, with a richly granular protoplasmic body-sub- 

 stance, surrounded by a thin hyaline layer, and enclosing, besides the 

 nucleus, one or more contractile vesicles. The Pseudopodia are finger- 

 like, sometimes lobose, processes, which become full of granules when they 

 attain a certain size, and which vary in number and breadth according 

 to the consistency of the body. 



The form of the body may be generally described as spherical ; 

 but this undergoes during life a continual Protean change, as the 

 animals flatten themselves out for movement, and then send out 

 pseudopodia, now here, now there, indifferently. The size and struc- 

 ture of the latter differ sometimes very characteristically in the 

 different species. When the protoplasm has only a comparatively 

 slight consistency, the animals seem almost to flow along on their 

 lower surface. The nature of the food varies according to circum- 

 stances, but in the free-living forms consists mainly of parts of plants. 

 These are enclosed by the movements of the protoplasm, and are 

 digested, the undigested residue being expelled by any part of the body 

 indifferently. The only mode of reproduction as yet distinctly ob- 

 served 3 is that of simple division, which is completed in a short time, 



the frog (Mutters Archivf. Anat. u. Physiol., Bd. viii., p. 12, 1854). They are sometimes 

 found in considerable numbers, and exhibit a somewhat rapid motion. Similarly, Walden- 

 berg found amo3boid animals in the intestinal canal of the rabbit, and once even inside an 

 epithelial cell (Archivf. pathol. Anat., Bd. xl., p. 438, 1867). Amoeboid parasites are also 

 not unfrequently found in the intestinal canal of insects, such as beetles, &c. 



1 See the classic investigations of de Bary on Myxomycetes, Zeitschr. f. wiss. ZooL, 

 Bd. x., p. 88, 1859 [and more recently Zopf, " Die Spaltpilze :" Breslau, 1883. W. E. H.] 



2 According to Cienkowsky, Archiv f. milcrosk. Anat., Bd. xii., p. 15, 1876. 



3 [More recently it has been demonstrated by the investigations of Maggi, Grassi, 

 Brass, and others, that Amoeba not only divide, but also, 'after encysting form swarm - 

 spores, which resemble Monads both in appearance and in movement. R. L.] 



