Chapter 19 

 Order 3 Amoebina Ehrenberg 



THE Amoebina show a very little cortical differentiation. There 

 is no pellicle or test, surrounding the body, although in some a 

 delicate pellicle occurs. The cytoplasm is more or less distinctly dif- 

 ferentiated into the ectoplasm and the endoplasm. The ectoplasm is 

 hyaline and homogeneous, and appears tougher than the endoplasm. 

 In the endoplasm, which is granulated or vacuolated, are found one 

 or more nuclei, various food vacuoles, crystals, and other inclusions. 

 In the freshwater forms, there is at least one distinctly visible 

 contractile vacuole. The pseudopodia are lobopodia, and ordinarily 

 both the ectoplasm and endoplasm are found in them. They are 

 formed by streaming or fountain movements of the cytoplasm. In 

 some members of this order, the formation of pseudopodia is erup- 

 tive or explosive, since the granules present in the endoplasm break 

 through the border line between the two cytoplasmic laj^ers and 

 suddenly flow into the pseudopodia. Asexual reproduction is ordi- 

 narily by binary fission, although multiple fission may occasionally 

 take place. Encystment is of common occurrence. Sexual reproduc- 

 tion, which has been reported in a few species, has not been con- 

 firmed. 



The Amoebina inhabit all sorts of fresh, brackish, and salt waters. 

 They are also found in moist soil and on ground covered with decay- 

 ing leaves. Many are inhabitants of the digestive tract of various 

 animals, and some are pathogenic to the hosts. 



The taxonomic status of the group is highly uncertain and con- 

 fusing, since their life-histories are mostly unknown and since numer- 

 ous protozoans other than the members of this group often possess 

 amoeboid stages. Forms such as Rhizomastigina (p. 263) may be 

 considered as belonging to either the Sarcodina or the Mastigophora. 



The order is subdivided into four families as follows: 



With amoeboid and flagellate stages 



Family 1 Dimastigamoebidae (p. 344) 



Amoeboid stage only 



With one or more nuclei of one kind 



Free-living Family 2 Amoebidae (p. 345) 



Parasitic. Family 3 Endamoebidae (p. 351) 



With a secondary nucleus Family 4 Paramoebidae (p. 371) 



343 



