FRESH-WATER RHIZOPODS. 



PROTOPLASTA. 



Froios, first ; plasso, I form or mould. 



The Protoplasta comprise by far the greater number of the Fresh- 

 water Rhizopods,. and include nearly all the known forms except the Heli- 

 ozoa, or Sun-animalcules. They are divisible into two sub-orders, the 

 liobosa and the FiJosa, founded mainly on the difference of the pseudo- 

 pods, which in the former are comparatively thick, finger-like or lobose, 

 and in the latter filamentous and of extreme delicacy. 



Some of the Protoplasts are naked, usually have no real distinction in 

 the relative position of parts, and emit pseudopods from any portion of the' 

 body-mass, though even most of these when in movement, for the time' 

 being, may have the body more or less differentiated into an anterior and a 

 posterior region. 



The greater number of the Protoplasts are provided with an exterior 

 shell, commonly of a more or less flask- or vase-like shape, and, with 

 few exceptions, having a single orifice, from which the pseudopods are 

 projected. The shell is an excreted membrane, chitinoid or siliceous in 

 character, or it is constructed of siliceous sand or particles of similar con- 

 stitution, but, so far as known, appears never to be composed of carbonate 

 of lime. 



PROTOPLASTA LOBOSA. 



The liObose Protoplasts, represented by the familiar Amoeba, 

 Difflugia, Arcella, as well as by many other less known genera, are princi- 

 pally characterized, as indicated in the name, from the comparatively thick, 

 lobe-like, or blunt finger-like form of the pseudopods. 



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