286 BIOLOGY OF THE PROTOZOA 



arboroid types; encystment is practically uni\^ersal; reproduction is 

 by longitudinal division while free-swinnning or encysted, or by 

 multiple division whereby a number of individuals are formed from 

 a single cell (somatella) within the membrane of the original cell 

 replacing a cyst wall. Nutrition is holozoic, saprozoic or osmotic 

 (parasitic) and with the parasitic forms, the effects on their hosts 

 vary from none at all to high mortality. 



Fertilization processes are practically unknown and the few obser- 

 vations extant have never been confirmed. 



Classification of the more primitive forms is still in a tentative 

 phase. Affinities are obscure in most groups and although some 

 appear to be natural others include heterogeneous forms which 

 will be sorted out as observations on life histories accumulate. 



Thus the general group of Protomonadina of Blochmann, Doflein, 

 and others, may include representatives of closely related forms 

 which in time will be recognized as sufficiently characteristic to 

 merit independent places in classification. This appears to be the 

 case with the Trypanosomatida^ where the life histories indicate a 

 close relationship of the genera Herpetomonas, Leptomonas, Leish- 

 mania, (^rithidia and Trypanosoma; or the group of collar-bearing 

 flagellates included in the earlier families Choanoflagellidse and Phal- 

 ansteriiche. These we raise to the value of sub-orders and give the 

 same value to the pseudopodia-bearing forms with permanent 

 flagella (Pantastomina), otherwise the classification adopted here 

 agrees closely with that used by Doflein, recognizing his Cysto- 

 flagellata, however, as Dinoflagellates, and we group the animal 

 flagellates into four orders: Pantastomatida, Protomonadida, 

 Polymastigida and Hypermastigida. 



Order I. PANTASTOMATIDA (Pantastomina of Minchin). 



The al)ility to protrutle pseudopodia is widely spread amongst 

 flagellates but this affords little justification for including such 

 forms with the Sarcodina. The formation of lobose pseudopodia 

 is an expression of the physical consistency of the cell protoplasm 

 and may occur in cells throughout the animal kingdom. The 

 possession of a flagellum throughout life is a distinct characteristic 

 and while such forms may be considered, with Ndgleria, as transi- 

 tional forms to the Sarcodina they are nevertheless to be classed as 

 flagellates while Xdc/leria with equal reason is to be classed with 

 other Amcebida in which the temporary flagella are regarded as 

 reminiscent structures. One argmiient, however, which may be 

 brought against this procedure is the life history of Mastif/ella 

 vitrea, which, as worked out by Goldschmidt (1905) includes chrom- 

 idia formation and fertilization phenomena which are undeniably 

 similar to those occurring in rhizopods. 



