SPECIAL MORPHOLOGY AND TAXONOMY OF SARCODINA 337 



budding division is typical of the testate forms and differs materially 

 from binary fission (see p. 217). Acceptable accounts of sexual 

 processes are limited to the Testacea in w^hich there is a general 

 resemblance to the type of gamete formation characteristic of the 

 Foraminifera (see Chapter V). 



Parasitic forms of the Amoebidae are widely distributed throughout 

 the animal kingdom. They are usually present in the digestive 

 tract but may be ectoparasites as well. The great majority are of 

 the nature of commensals and are harmless, some, however, are 

 pathogenic as Amoeba mvcicola, Chatton, a harmful ectoparasite on 

 the gills of Labrida^, or Endamoeha dysenierioB, Craigia hominis, and 

 Councilmania lafleuri, Kofoid, causes of dysentery in man. 



The organisms included in the Amoeba^a fall naturally in one of 

 two groups which have been generally recognized as Amoebida 

 (Gymnamrebida) and Testacea. Following the principle adopted 

 in classifying the Mastigophora where amoeboid forms of animal 

 flagellates are retained as IVIastigophora only when the flagellum or 

 flagella are permanent structures of the organism, we include as 

 rhizopods those forms with pseudopodia and temporary flagella; 

 flagella and pseudopodia being more or less interchangeable. These 

 are included here in the family- Bistadiidse of Doflein. 



Order 1. Amoebida (Gymnamoebida), Ehrenberg. 



Naked forms of amoeba^a, either free-living or parasitic; with one 

 or more nuclei ; with contractile vacuole (except in some of the para- 

 sitic forms); reproduction by binary fission, multiple division 

 occasional. Encystment widespread. 



We recognize four families in this order, liz.: Bistadiidse, Amoe- 

 bida^, Endamoebida? and Paramoebida^. Separation of the parasitic 

 forms of amoebte from free-living forms is hardly justifiable in a 

 natural classification but is tolerated on grounds of expediency. 



Family 1. Bistadiidae, Doflein.— Organisms characterized by two 

 interchangeable phases— amceboid and flagellated. In the former 

 phase the body is amoeboid with lobose pseudopodia. A single 

 nucleus with endobasal body is present; the basal body of the 

 flagellum is formed by division of the endobasal body (Wilson) 

 and the flagellum grows out from the basal body. Transformation 

 from the amceboid to the flagellated condition involves loss of amoe- 

 boid movement and change in form to a monaxonic ellipsoidal form. 

 Absorption of the flagellum accompanies transformation again to 

 the amoeboid condition. These changes are e\'identl\^ induced by 

 environmental conditions and, in cultural forms, may be brought 

 about at will. Genera with one, two, and three flagella in the 

 flagellate phase are known. Reproduction by division limited to 



