INTRODUCTION 



35 



change in mode of life, well illustrated by Bimorpha mutans (Fig. 13), 

 by Bimastigamoeba gruberi or Trimastigamoeba. Fantastic types 

 such as Biscomorpha pectinata or Tripalmaria dogieli (Fig. 14) 

 are not uncommon and no evident connection between such bizarre 

 forms and their mode of life is apparent. 



Methods of food-getting and the nature of the food are also potent 

 factors in determining form. Many of the diatom- and desmid- 

 eating eiliates, whose food lies on the 

 bottom, are characteristically flattened 

 forms with the mouth on the under, or 

 physiological ventral, surface (holotrich- 

 ous eiliates belonging to the genera 

 Chilodon, Orthodon, Opisthodon, Chlamy- 

 dodon, Loxophyllum, etc., and the major- 

 ity of the hypotrichous eiliates) . Special 

 food-getting, or current-directing, organs 

 frequently modify the form as in the 

 collared flagellates (Choanoflagellates) 

 and in types like Folliculina ampulla 

 (Fig. 94, p. 169), Bursaria truncatella 

 (Fig. 94, p. 169), cephalont gregarines, 

 Pleuronema (Fig. 199, p. 482), etc. Shift- 

 ing of the position of the mouth in re- 

 sponse to different food requirements, 

 as Biitschli has shown, has undoubtedly 

 been the cause of some form changes. 

 Thus the proboscis-bearing species and 

 the asymmetrical Chilodon types may 

 owe their characteristic forms to such a 

 shifting of the oral region (Fig. 15). 



The monaxonic types, while typically ellipsoidal in form, are 

 frequently characterized by a spiral twisting of the cell body, espe- 

 cially in the rapidly moving forms. In some cases, notably in the 

 flagellates Streblomastix, Spiromonas, Holomastigotes, etc., and in 

 the eiliates Aegyria, Paramecium, Metopus sigmoides, etc., the spiral 

 twist is highly characteristic (Fig. 16). 



Bilateral symmetry is of rare occurrence among Protozoa; indeed 

 there seem to be few significant cases, that of Giardia being the 

 best known (Fig. 17). Here the two nuclei, the motor complex and 

 the eight flagella are arranged in the neatest bilateral manner. One 

 possible mode of origin of such bilaterally symmetrical types is 

 indicated by Uroleptus mobilis (Fig. 18). Here two individuals, after 

 conjugation, fused to form a single double and bilaterally symmetri- 

 cal individual which persisted through 367 generations (see also 

 Fig. 127, p. 245). 



Form may be dependent also upon the mode of reproduction. 



Fig. 14. — Tripalmaria" dogieli 

 (minor). Gut parasite of the 

 horse with three bundles of cilia 

 and internal skeleton. X 520. 

 (After Strelkow, Arch. f. Pro- 

 tistenkunde, courtesy of G. 

 Fischer.) 



