CHAPTER XVII 



ORDER 4 AMOEBAEA EHRENBERG 



THE AMOEBAEA show a Very little cortical differentiation. 

 There is no pellicle, test, or shell surrounding the body, 

 although in some, such as Amoeba verrucosa, the surface seems 

 to be much hardened. The cytoplasm is more or less distinctly 

 differentiated into the ectoplasm and the endoplasm. The ecto- 

 plasm is hyaline and homogeneous, and appears tougher than 

 the end6plasm. In the endoplasm, which is granulated or 

 vacuolated, are found one or more nuclei, various food vacuoles, 

 water vacuoles, crystals, and other bodies. In the fresh-water 

 forms there is at least one distinctly visible contractile vacuole. 

 The pseudopodia are lobopodia, and ordinarily both ectoplasm 

 and endoplasm are found in them. They are formed by stream- 

 ing or fountain movements of the cytoplasm. In some members 

 of the order, the formation of pseudopodia is described as erup- 

 tive since the granules which are found in the endoplasm break 

 through the border line between the ectoplasm and the endo- 

 plasm and suddenly flow into the pseudopodia. 



The life-history is not completely known, even among such 

 common forms as Amoeba proteus. Asexual reproduction is 

 ordinarily binary fission, although occasionally multiple fission 

 takes place. Encystment is common for both free-living and 

 parasitic forms. Sexual reproduction, which has been reported 

 for a few species, has not been confirmed. 



The Amoebaea inhabit all sorts of fresh, brackish and salt 

 waters. They are also found in most soil and on ground covered 

 with decaying leaves. Many are inhabitants of the digestive 

 tract of various animals, and some of them are pathogenic. 



The taxonomic status of the group is highly uncertain and 

 confusing, since their hfe-histories are mostly unknown and 

 since numerous Protozoa other than the members of this group 

 often possess amoeboid stages. Forms such as Pantostomatida, 

 may rightly be considered as belonging to either the Sarcodina 



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