Chapter 19 

 Order 3 Amoebina Ehrenberg 



THE Amoebina show a very little cortical differentiation. There 

 is no thick pellicle or test, surrounding the body, although in 

 some a delicate pellicle occurs. The cytoplasm is more or less dis- 

 tinctly differentiated into the ectoplasm and the endoplasm. The ec- 

 toplasm 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 ordi- 

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

 are formed by streaming or fountain movement 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 layers 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. 



The order is subdivided into four families as follows: 



With amoeboid and flagellate stages 



Family 1 Naegleriidae 



Amoeboid stage only 



With one or more nuclei of one kind 



Free-living Family 2 Amoebidae (p. 437) 



Parasitic Family 3 Endamoebidae (p. 443) 



With a secondary nucleus Family 4 Paramoebidae (p. 405) 



Family 1 Naegleriidae 



The members of the two genera placed in this family possess both 

 amoeboid and flagellate phases [diphasic). In the former, the organ- 



435 



