370 GENERAL ZOOLOGY 



saprophytic, i.e., capable of living on dead or decaying organic 

 material. The cytoplasm consists of a clear outer layer, the 

 ectosarc, and an inner region, the endosarc, in which lie 

 the nucleus, chromatophores, and contractile vacuoles. The 

 nature and action of the contractile vacuole are considered in 

 connection with Amoeba, in which it can be more readily 

 studied (p. 372). During encystment Euglena secretes a thick 

 gelatinous envelope about itself and assumes a spherical form. 

 Euglena may reproduce (1) in the free state by longitudinal 

 fission; (2) by conjugation, a method described in detail in 

 connection with paramecium (p. 382); and (3) during encyst- 

 ment by binary or multiple fission. 



SUBCLASS 2. ZOOMASTIGOPHORA. Animal-like flag- 

 ellates, lacking chromatophores and living as solitary or 

 colonial forms under holozoic, saprozoic, or parasitic conditions. 

 Examples: Trypanosoma gambiense, a blood parasite, the 

 cause of sleeping sickness among human beings in Western 

 and Central Africa. It is transmitted by the bite of a tsetse 

 fly, Glossina palpalis. T. lewisi, another species, is trans- 

 mitted to rats by fleas. Codosiga, a colonial form, each member 

 of the colony being provided with a collarlike ridge surrounding 

 the base of the flagellum (Fig. 204). 



CLASS II. SARCODINA. Protozoa whose body lacks a firm 

 pellicle, in consequence of which change of body shape is 

 possible. Some have shells. 



SUBCLASS 1. RHIZOPODA. Creeping forms with root- 

 like PSEUDOPODIA. 



Order 1. Amoebida. Naked forms found in fresh and salt 

 water, soil, and as parasites in the alimentary canal of Metazoa. 

 Contractile vacuoles are present except in salt-water forms. 



Examples: Amoeba proteus, a common fresh-water form; 

 Endamoeba histolytica, parasitic in the human colon, causing 

 dysentery and ulcers in the liver. 



Amoeba proteus, examined on a slide under the microscope, 

 appears as an irregular, jellylike mass of protoplasm, slowly 

 changing its outline by projecting pseudopodia (Fig. 205). 

 Its size varies from about 127 to 340 fj, in diameter. The 

 action of the pseudopodia in bringing about movements can 

 best be understood if the amoeba is viewed from the side 

 instead of from above. To do this, the amoeba is placed in 



