The Mastigophora 171 



cycles are known, as in the Trypanosmidae, and sexual phenomena have 

 been reported in a few instances, most recently by Cleveland (Chapter II). 



Present classifications are tentative at best and are based, to an im- 

 portant extent unfortunately, upon somewhat artificial criteria rather 

 than upon detailed information which might suggest natural relation- 

 ships. The recent erection of the order Trichomonadida (147), the result 

 of a long series of intensive studies, has set a sound pattern for the pos- 

 sible establishment of additional coherent orders within certain areas of 

 the class. In the meantime, the remnants of the "Polymastigida" may 

 be retained, along with the other older orders, for taxonomic convenience. 

 Accordingly, the Zoomastigophorea may be subdivided as follows: 



Order I. Rhizomastigida. This inadequately defined group of amoe- 

 boid flagellates has served occasionally as a repository for genera of un- 

 certain taxonomic position, and has also been treated as a family of the 

 Protomastigida. 



Order 2. Protomastigida. These are solitary or colonial types with one 

 or two fiagella. The body is plastic but does not show the amoeboid 

 activity of the Rhizomastigida. 



Order 3. Polymastigida. The remnants of the old Order Polymastigida 

 include mostly uninucleate and binucleate species, although there are a 

 few with a number of nuclei. There are usually 3-8 fiagella. 



Order 4. Trichomonadida. These are uninucleate or multinucleate 

 (but not binucleate) flagellates with an axostyle, a parabasal body, and 

 a mastigont of 3-6 fiagella. One of the fiagella is typically a trailing fiag- 

 ellum which may or may not form part of an undulating membrane. 



Order 5. Hypermastigida. These are uninucleate flagellates with many 

 fiagella. The known sjoecies are intestinal parasites of termites, wood 

 roaches and cockroaches. 



Order 1. Rhizomastigida 



This order may be limited to flagellates with 1-4 fiagella and 

 amoeboid bodies which often show considerable pseudopodial activity. 

 In at least some species, a cytoplasmic fibril ("rhizostyle") of uncertain 

 significance extends posteriorly from one of the blepharoplasts. 



The following genera may be assigned to the order: Heliobodo Valkanov (276; Fig. 

 4. 39, I); Histomonas Tyzzer (20, 273, 274, 280; Fig. 4. 39, A-F); Mastigamoeba Schulze 

 (153); Mastigella Frenzel (88, 97, 153; Fig. 4. 39, L); Mastigina Frenzel (12, 13, 88; Fig. 

 4. 39, J, K); and Rhizomastix Alexeieff (191; Fig. 4. 39, G, H). Tricholimax Frenzel 

 apparently is a synonym of Mastigina Frenzel (97). Certain other genera, sometimes 

 included in the Rhizomastigina, probably do not belong here. Pteridomonas Penard 

 possibly should be referred to the Chrysomonadida, while Actinomonas Kent and 

 Dimorpha Gruber probably belong in the Helioflagellida (Chapter V). The relationships 

 of Multicilia Cienkowski (177) are uncertain on the basis of available data. Although 

 the body is amoeboid, the many fiagella (or axopodia?) and the 1-4 nuclei are not very 

 strong inducements for retaining this genus in the Rhizomastigida. 



