MORPHOLOGY AND TAXONOMY OF THE MASTIGOPHORA 417 



complex motile organs for movement. Duboscq and Grasse hom- 

 ologize the parabasal with the idiosome of spermatozoa which is 

 regarded as a Golgi element, while Grasse (1925) interprets the 

 parabasals in Trichomonas batrachorum and Tetramastix bufonis as 

 secretory in function, forming minute droplets which break up into 

 smaller elements for distribution in the cytoplasm. Brown (1930), 

 more recently, dissents from this interpretation and finds no evi- 

 dence in Dinenympha or Pyrsonympha to support the view that 

 parabasals are homologous with the Golgi apparatus. The latter 

 is present, however, in the form of distributed spherical bodies, 

 which may appear as crescents or rings and which are believed to 

 be secretory in nature. When the granules are present, a Golgi 

 network is absent or much reduced, but a typical network appears 

 at times at the base of the axostyle (Fig. 176). 



These diverse points of view leave us very much in the air in 

 regard to the chemical nature and function of the parabasal body 

 so conspicuous in the parasitic flagellates. Their variations in size 

 and shape in the same species certainly indicate their connection 

 with some urgent metabolic need, but for the present at least the 

 nature of this need is enigmatical. 



Nuclei are not especially characteristic. In Protomonads it is 

 usually of the centronucleus type— with endosome and frequently 

 with endobasal body (see p. 60). In more complicated flagellates 

 (Polymastigida and Hypermastigida) the endosome becomes 

 greatly reduced or absent altogether and no longer contains the 

 centriole. The latter is either on the nuclear membrane or as a 

 blepharoplast near to it, and, during nuclear activity, it divides 

 with a connecting strand. This strand is homologous with the 

 intranuclear centrodesmose of simpler types, but remains outside the 

 nucleus as a paradesmose (Fig. 54, p. 100). Here, therefore, we have 

 evidence of a permanent separation of chromatic and kinetic com- 

 ponents of the nucleus, the latter now being permanent cytoplasmic 

 structures. A peculiarity of the chromosomes in some cases is the 

 apparent reduction to one-half the normal number during mitosis 

 (Giardia microti, Boeck, 1917; Trichonympha campanula, Kofoid 

 and Swezy, Fig. 54, p. 100), although with the possible exception of 

 Helkesimastix, Woodcock and Lapage (1915) no fertilization proc- 

 esses are safely established for any type of animal flagellate. 



Contractile vacuoles are generally distributed in the free-living 

 forms, where they are invariably simple vesicles. In parasitic forms 

 they are generally absent. 



Reproduction of flagellates is typically by simple longitudinal 

 division. In free-living forms the individual in many cases remains 

 connected by stalk-like processes (Poteriodendron, Fig. 177), or by 

 dichotomously branched gelatinous tubes (Cladomonas) or laterally 

 cemented tubes (Rhipidodendron). In some cases they are embed- 

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