THE MASTIGOPHORA 



271 



Flu. 114. Cercomonas crassicauda, Dujardin, 

 showing amoeboid changes of form. After 

 Stein. 



recently described by Wenyon (361) from a culture of human faeces, and 

 referred by him to the genus Cercomonas, would appear rather to belong to 

 the genus Bodo. To the family Bodonidce must be referred also the genera 

 Prowazekia and Trypanoplasma, dealt with in greater detail in the next chapter. 

 Helcomastix, Senn (358), is to 

 be referred to the Bodonidce or 

 made the type of a distinct 

 family; its two flagella of 

 unequal length are both 

 directed backwards in move- 

 ment. 



Finally, mention must be 

 made of the group of flagel- 

 lates characterized by the pos- 

 session of a collar (see p. 261, 

 supra), and hence commonly 

 known as " choanoflagel- 

 lates" or " craspedomonads." 

 They are sedentary forms, 

 attached by the end of the 

 body opposite to the flagellum, 

 and may remain single, but 

 more usually form colonies 

 often of considerable extent 

 (Fig. 110). The flagellum is 

 used mainly for food-capture, 

 in which the collar also pro- 

 bably plays an important 

 part ; but an individual may 

 become detached from its 

 support, and swim freely, the 



flagellum being then directed backwards. The systematic position of the 

 choanoflagellates has been differently estimated by different authors ; by some 

 they have been ranked as a primary subdivision of the Flagellata, which are 

 then divided as a whole into Choanoflagellata and Lissoflagellata, the second 

 of these divisions being used to include all other flagellates. Since, however, 



the choanoflagellates scarcely differ from ordinary monads 

 except in the possession of the characteristic collar, a 

 specialization of the food- capturing function related to 

 a sedentary life, they are now generally ranked as a 

 family of the Protoinonadina, the Choanoflagdlidce. 



ORDER III. : POLYMASTIGINA. Flagella from three to 

 eight in number, usually all more or less equal in size ; 

 in other points of structure similar to the last-mentioned 

 order. Two families, which are sharply marked off from 

 one another, are referred to this order. 



1. Tetramitidce, with three or more flagella, which all 

 arise at. the anterior end close together. The flagella 

 may all be directed forwards, or one of them may be 

 turned backwards as a trailing flagellum ; in the latter 

 case the trailing flagellum may or may not be united to 

 the body by an undulating membrane. 



The species referred to this family are for the most 



' 7 * O J. * 



graciLis, k_ n. part parasitic. Endoparasitic forms of common occur- 

 After Stem. rence, especially in the digestive tracts of vertebrates, 



are Trichomaatix, with three anterior flagella and a free 

 trailing flagellum, and Trichomonas (Fig. 5), with the same number and arrange- 

 ment of the flagella, but having the trailing flagellum united to the body by an 

 undulating membrane. These two forms occur frequently in the same host, 

 and are perhaps to be interpreted as two developmental phases of the same 



FIG. 115. A Bode 

 saltans, Ehren- 

 berg. B. Bodo 



