AMCEBA PROTEUS VS. ENDAMCEBA COLI 



The phylum Protozoa is usually divided into four 

 classes, Sarcodina, Mastigophora, Sporozoa and In- 

 fusoria. The Sporozoa are all parasitic; the other three 

 classes include both free-living and parasitic species. It 

 seems probable that the parasitic habit has evolved from 

 the free-living habit independently in each of these three 

 classes, and this type of evolution has no doubt taken 

 place many times within each class. Changes from a 

 marine to a fresh-water habitat and vice versa, involving 

 the formation of new species, have doubtless similarly 

 occurred among free-living species. 



Amoeba proteiis vs. Endamocha coli. The most common 

 amoeba of man is Endamceba coli, which lives in the lumen 

 of the large intestine and occurs in about 50 per cent of 

 the general population. The best known free-living 

 amoeba is Amoeba proteus. Morphologically these two 

 species resemble each other very closely. Both consist of 

 cytoplasm, which is differentiated into an external layer 

 of clear ectoplasm and an internal mass of granular 

 endoplasm. Both possess a single nucleus; the nuclei of 

 the two species differ from each other in shape, size and 

 the distribution of the chromatin, but the differences are 

 no greater than those between nuclei of species belong- 

 ing to different genera of free-living amoebae. Both carry 

 on locomotion and capture food by means of pseudo- 

 podia; and there is no reason to believe that the funda- 

 mental process of amoeboid movement differs in the two 

 species. 



The food of both species consists, so far as we know, 

 of solid particles in the medium in which they live, and 

 these food substances appear to be selected in both species ; 



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