26 PROTOZOA 



ORDER 1. SPIROCHETIDA. 



Body elongate, spiral, with or without an undulating membrane; 

 flagellum very short or absent; nucleus diffuse: 1 family. 



FAMILY SPIROCHETIDAE. 



With the characters of the order: 3 genera. 

 1. SPIROCHETA Ehrenberg. Undulating membrane but 

 no flagellum present: about a dozen species; 

 mostly parasitic. 



S. balbianii (Certes) (Fig. 20). Length .02 

 to .18 mm.; broad membrane present; ends 

 rounded: in the digestive tract of the oyster, 

 often in the crystalline style. 



S. plicatilis Ehr. (Fig. 21). 

 Length .08 to .2 mm.; narrow 

 membrane present; ends rounded: 

 in stagnant water. 



2. TREPONEMA Schaudinn. Fla- 

 gellum but no undulating mem- 

 Fig. 21 Sptrocheta plica- 



tili* (Doflein). brane present: about 8 species. 



T. pallidum Schaudinn (Fig. 22). Body cylindrical, without 

 membrane, .015 mm. long ; ends tapering, ending each in a fine flagellum : 

 in syphilitic lesions. 



ORDER 2. MONADIDA. 



Body usually without shell and more or less amoeboid, with 1 or 2 

 large flagella at the forward end and often 1 or more secondary flagella ; 

 no mouth : 5 families. 



Key to the families of Monadida here described: 



Ci Pseudopodia present 1. RHIZOMASTIGIDAE 



2 Pseudopodia absent, 

 fcj One flagellum present. 



G! Body not in a cup 2. CEBCOMONADIDAE 



c, Body in a cup 3. CODONECIDAE 



6 a Two flagella present 4. HETEROMONADIDAE 



FAMILY 1. RHIZOMASTIGIDAE. 



Simple forms without mouth and with 1 or 2 flagella; occasionally 

 with either lobose pseudopodia like a rhizopod or stiff radial ones like 

 a heliozoan; food taken at any part of the body: 6 genera. 



MASTIGAMCEBA F. E. Schulze. Body irregular in form with several 

 pseudopodia which disappear when the animal swims, and one long 

 flagellum: 6 species; in fresh and salt water. 



