Chapter 18 

 Order 3 Amoebina Ehrenberg 



THE Amoebina show a very little cortical differentiation. 

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

 in some there are indications that a very thin and delicate pellicle 

 exists. The cytoplasm is more or less distinctly differentiated into 

 the ectoplasm and the endoplasm. The ectoplasm is hyaHne 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 

 described as eruptive 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. 



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

 species of the genus Amoeba. Asexual reproduction is ordinarily 

 by binary fission, although multiple fission may occasionally take 

 place. Encystment is of common occurrence. Sexual reproduction, 

 which has been reported in a few species, has not been confirmed. 



The Amoebina inhabit all sorts of fresh, brackish and salt 

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

 with decaying 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 

 numerous protozoans other than the members of this group often 

 possess amoeboid stages. Forms such as Rhizomastigina (p. 235) 

 may be considered as belonging to either the Sarcodina or the 

 Mastigophora. 



The order is subdivided into three families as follows : 



With amoeboid and flagellate stages 



Family 1 Dimastigamoebidae (p. 305) 



304 



