548 STSTEilATIC HISTORY OF THE INFrSORTA. 



of signification is ill-defined. Some would apply it to the whole collection of 

 animalcules composed, as far as their organic material is concerned, of the 

 self- same simple homogeneous sarcode, whether this exist naked, as in the 

 Amoebaea, or whether enclosed within a simple single-chambered shell, as in 

 the Monothalamia, or in a many-chambered or compound one, as in the Poly- 

 thalamia or Foraminifera. Siebold extends to the Rhizopoda, as a class, this 

 wide signification. Others, and among them Ehrenberg, would so far limit 

 it as to assign to it only the naked Amoebaea and the monolocular Arcellina. 

 Indeed, the last-named author holds the opinion of an actual difi'erence in 

 organic nature between his presumed Polygastric Pseudopoda and the Fora- 

 minifera or Polysomatia. Dujardin adopted the peculiar coiu'se of rejecting 

 the Amceba^a from the Ehizopoda, which in his system, included both mono- 

 locular and multilocular forms. In our general history of the Ehizopoda 

 (p. 201), we have used the term in its widest signification, to include naked 

 monolocular and multilocular beings ; but, in order to keep this systematic 

 portion of our work within moderate bounds, we shall here give only the 

 descriptive accoimt of the Amoebaea and ArceUina. Were another reason 

 required than that assigned for this proceeding, a strong one might be found 

 in the fact of the approaching completion of an elaboi^ate work on the Pora- 

 minifera by Professors Williamson and Carpenter, who are so well kno^Ti for 

 their extensive acquaintance with this class of organisms. 



Families: — I. Amoebaea ; 2. Monothalamia (Arcellina); 3. Polytha- 

 lamia (Foraminifera); 4. Actinophryina ; 5. Acinetina. 



FAMILY I.— AMCEBJEA on AMCEBINA. 



The Amcebaea present the simplest form of organic life, and are typically 

 represented by a microscopic particle of ' sarcode,' or muco-gelatinous organic 

 matter, possessing within itself the power of growth, of assimilation of ex- 

 traneous substances, of movement by means of irregular and ever-changing 

 offshoots from itself — " variable processes," — and capable of multii^lication by 

 the severance of portions of itself, and probably of development by internal 

 germs or gemmules. They present no definite, constant figiu-e, although it is 

 possible to distinguish different Amoebaea by the more frequent outline they 

 exhibit, or by the length or figm^e of theii' pseudopodes. The general opinion 

 is that the sarcode of which they consist is naked and homogeneous ; but 

 Auerbach (see ante, p. 205) has advanced the statement that they are all en- 

 closed ^TLthin an integument. A movement of granules is perceptible, espe- 

 cially along the margins of the variable processes. A nucleus with a nucleolus is 

 believed to be generally present ; vacuoles are almost always distinguishable ; 

 and one, two, or even more contractile vesicles have been seen in some speci- 

 mens. There seems evidence of the process of encysting taking place under 

 certain conditions. Amoebiform beings are not necessarily of an animal nature ; 

 for some have latterly been proved to occur in the cycle of development of some 

 of the simplest plants. Ehrenberg described Amoebaea as polygastric ani- 

 malcules, ha^dng a mouth but no alimentary canal, and mo"sdng by variable 

 processes, produced from any part of the body indiff'erently. He observed 

 vacuoles (digestive sacs) in all, and sclf-di\ision in Amoeba diffluens. The 

 Amoebaea are organically related to the Arcellina and Foraminifera, from 

 both of which groups they differ by being naked, or unenclosed in a shell 

 (see p. 234). 



Only one genus is distinguishable, viz. 



Genus AMCEBA, which is therefore represented by the description of the 



