268 THE PROTOZOA 



are a certain number of well-defined orders and families characterized by 

 the possession in common of certain features of organization which leave 

 no doubt as to their taxonomic homogeneity. On the other hand, there are 

 a large number of primitive forms whose characteristics are mainly of a 

 negative order, and of which the affinities are in consequence vague and 

 uncertain, the systematic position debatable. There is, moreover, frequently 

 an element of uncertainty, in the case of many forms, as to whether they 

 represent truly specific adult forms, or merely developmental stages of some 

 other soccies of the Flagcllata or Sarcodina. Finally there are a certain 

 number of species and genera concerning which it is still debated whether 

 they should be assigned to the Mastigophora or some other class of Protozoa. 



Hartmann and Chagas (62) have proposed to utilize the relations of the 

 flagellar to the nuclear apparatus for systematic classification of the FlageUata, 

 as suggested also by Prowazek (354). But, apart from the fact that these 

 relations have as yet been investigated in very few flagellates, and that in 

 such minute objects the details are very difficult to make out and liable to 

 be a subject of dispute, it may be doubted whether these points of structure 

 are sufficiently constant to be of classificatory value in this subclass, since 

 they appear to vary considerably in allied forms. Thus in Copromonas 

 subtilis, according to Dobell (335), the blepharoplast persists through division- 

 phases, and divides independently of the nucleus ; but in C. major, according 

 to Berliner, the old blepharoplast and flagellum are lost at each division, 

 and a new blepharoplast, from which the new flagellum grows out, is formed 

 by division of the nuclear centriole in each daughter-individual. Again, the 

 third type of flagellar insertion (p. 263) is found in the Trypanosomidce, allied 

 to the Cercomonadidce, and in the trypanoplasms, which belong to the family 

 Bodonidce, as shown in the next chapter. Classification by these characters 

 is, therefore, at least premature, if not fallacious. Compare also Senn (358). 



The classification adopted here is in the main that of Doflein (7), with 

 certain modifications. For convenience a number of forms are put together 

 in the Pantastomina, without, however, claiming that this order is anything 

 more than a cataloguer's makeshift for disposing of a number of forms of 

 dubious position and uncertain affinities. 



ORDER I. : PAKTASTOMINA. Holozoic, with no definite mouth-opening ; 

 food-particles ingested at any point on the surface of the body. 



Suborder 1 : Rhizomastigina. Body amoeboid ; food captured and ingested 

 by means of pseudopodia. 



Several genera, only known as yet from fresh water, are referred to this 

 very interesting group ; such are Mastigamoeba, F. E. Schulze, Mastigina, 

 Frenzel (Fig. 38), and Mastigetta, Frenzel (Fig. 40), distinguished from one 

 another by the nature of their amoeboid movement and the characters of their 

 pseudopodia. In appearance the species resemble amoebae which possess a 

 long and well-developed flagellum, or in Dimastigamoeba two, in Trimastig- 

 amceba (Whitmore, 280) three flagella. Locomotion and food-capture are 

 carried on for the most part as in an amoeba, and the flagellum appears to 

 function chiefly as a tactile organ in the adult mastigamoeba-phase ; in the 

 young monad- phase, on the other hand, the flagellum is the sole organ of 

 locomotion and food-capture, as in an ordinary flagellate. The relation of 

 the flagellum to the nucleus is of Type 1 described above (p. 263), a single 

 centriole which functions both as centrosome and blepharoplast ; in Mastigina 

 and Mastigamoeba the flagellum arises from the nucleus (Type la) ; in Masti- 

 getta the origin of the flagellum is distinct from the nucleus (Type 16). The 

 life-cycle of Mastigetta is described above (p. 265). In many points, especially 

 in the formation of secondary gamete-nuclei from chromidia, the develop- 

 ment resembles more that of the Sarcodina than that of the Flagellata, and 

 by many authorities the affinities of the Rhizomastigina are considered to be 

 rather with the first of these two classes. The mastigamoebae certainly link 

 the true flagellates with the Proteomyxa and Mycetozoa ; and if the flagellum 

 were lost in the adult phase, they would be classed in the Sarcodina without 

 hesitation. 



