CHAPTER Xn 



ORDER 3 POLYMASTIGIDA BLOCHMANN 



THE zooMASTiGiNA grouped here possess three to eight 

 flagella and, generally speaking, are minute forms with 

 varied characters and structures. The majority inhabit the 

 digestive tract of animals. Many possess a cytostome. One 

 to many nuclei occur. The body is usually covered by a 

 thin pellicle and, therefore, is somewhat plastic, although each 

 species shows a more or less typical form. The cytoplasm does 

 not show any special cortical differentiation. In many, there 

 is an axial structure known as the axostyle or axial filament 

 (p. 39). Parabasal body is invariably present and shows various 

 forms. Contractile vacuole is generally absent. Nutrition is 

 holozoic, saprozoic, or parasitic. 



Asexual reproduction is by longitudinal fission, sometimes 

 multiple. Encystment is common, and the cyst is responsible 

 for infection of new hosts through the mouth. Sexual reproduc- 

 tion has not been definitely established. Some of the Poly- 

 mastigida have recently been studied rather extensively by 

 numerous investigators, but it is, as Calkins set forth clearly, 

 impossible to place them in definite genetically related groups. 

 Calkins' scheme is adopted in subdividing them into the follow- 

 ing three tribes: 



With one cytostome and kinetic element Tribe 1 Monozoa 



With two cytostomes and kinetic elements Tribe 2 Diplozoa 



With numerous nuclei and kinetic elements Tribe 3 Polyzoa 



Tribe 1 Monozoa Calkins 



Without cytostome and undulating membrane 



Without axostyle Group 1 



With axostyle Group 2 



With cytostome 



Without undulating membrane; with axostyle Group 3 



With undulating membrane 



Without axostyle Group 4 



With axostyle Group 5 



[155] 



