MORPHOLOGY AND TAXONOMY OF THE MASTIGOPHORA 41l> 



(see p. 141), they vary widely in number, size and arrangement on 

 the organism. The most generalized types have 1 flagellum which 

 is directed forward (Herpetomonas, Leishmania, Crithidia, etc.). 

 When 2 are present they may be similar in length and in orienta- 

 tion (Amphimonadidae) or of dissimilar length and oriented in the 

 same direction (Monadidae) or they may be oriented in different 

 directions (Bodonidae, Embadomonadidae, Cercomonas, etc.). 

 One of the 2 may be adherent to the body (Cercomonas), or, re- 

 tained by the periplast, forms the margin of an undulating mem- 

 brane (see p. 142) as in Trypanoplasma, Cryptobia, Trypanophis, 

 etc. If 3 flagella are present, 1 is directed anteriorly while 2 are 

 trailing flagella (Trimastix, Dallingeria, Macromastix). When 4 

 are present, all may be directed anteriorly (Tetramitns, Copro- 

 mastix, Polymastix) ; or one may be trailing (Eutrichomastix, 

 Retortamonas) or retained within a buccal furrow or cytostome, 

 while 3 are directed forward (Chilomastix) . In some forms the 

 trailing flagellum may be attached to the periplast (Tricercomitus) 

 or it forms an undulating membrane (Trichomitns, some species of 

 Trichomonas). In some forms there are 4 or 5 anterior flagella 

 and an undulating membrane (Trichomonas). In another group 

 of forms the single flagellum forms an undulating membrane (Try- 

 panosoma, Myxomonas). Myxomonas (Dogiel) may even lose its 

 undulating membrane and turn into an ameboid wood-eating 

 form. 



In one group of flagellates (diplozoic forms), including both 

 free-living and parasitic types., the organisms are bilaterally sym- 

 metrical. These interesting forms have two sets of flagella placed 

 symmetrically and 1 or 2 nuclei. They are supposed to have arisen 

 by reason of the suppression of cell division after the nucleus and 

 kinetic centers have divided. Similar double forms occur amongst 

 the ciliates where, by treatment with chemicals or ultra-violet rays 

 during division stages, cytoplasmic division is prevented (Glaucoma, 

 Chatton), or by union during conjugation double individuals result 

 (Uroleptus, see p. 245). Free-living diplozoic forms include Gyro- 

 monas, Trigonomonas, Trepomonas, Ilexamitus and Urophagus 

 and 2 genera of parasitic forms — Giardia and Octomitus. The 

 flagella are 4 in number in Gyromonas, 6 in Trigonomonas and 8 in 

 Hexamitus, Trepomonas, Urophagus, Octomitus and Giardia (Fig. 

 17, p. 37). 



A multiple number of flagella is quite characteristic of parasitic 

 Mastigophora, particularly parasites of the white ants (Termites). 

 Such polymastigote forms may have a single nucleus (monozoic 

 Hypermastigidae) or many nuclei (polyzoic types). The latter, 

 like diplozoic forms above, are supposed to have arisen by multiple 

 division of the nucleus and kinetic complex without accompanying 

 cell division (somatella stage). According to Janicki (1915), each 



