PKOTOZOA 



17 



infusions. It possesses a single anterior flagellum, and the 

 posterior pole is pointed and may be produced into a long 

 appendage, and, as has been said, this pole may present 

 pseudopodial processes as well. The latter are formed usually 

 as a preparation for conjugation. Eeproduction takes place 

 by longitudinal fission, and after a season conjugation takes 

 place by equal-sized individuals, and such are termed 

 isogametes. Mastigamoeba and its allies are still more 

 intermediate in character between 

 the amoeboid and flagellate Pro- 

 tozoa. 



General Considerations relating to 

 the Protozoa. The cell may be 

 studied from several different but 

 related aspects. It has a form and 

 structure which are reproduced 

 with great constancy generation 

 after generation. It has a form 

 which can be defined ; it can be 

 compared with other forms of cells 

 and the structures which determine 

 the form specified. This study 

 constitutes Morphology ; in this 

 case cell morphology. The cell is 

 living, and life is manifested by 

 movements and processes the study 

 of which in Protozoa and Metazoa is 



called Physiology. During its life, moreover, the cell responds 

 to stimuli of various kinds, and in the free state exhibits a 

 behaviour with respect to these the study of which lies in the 

 domain of Psychology. 



Morphology. It has been said that the living cell has a 

 form and a structure which are apparently constant, but we 

 have already seen that in addition to the living protoplasm 

 there are food constituents and waste materials, that water is 

 essential, and that a certain amount of change is constantly 

 taking place connected with the liberation of energy and the 

 building-up processes necessary to compensate for the loss. 



FIG. 8. Cercomonas, after 

 Stein. The flagellum is 

 anterior, and the tail pro- 

 cess and the pseudopodia 

 posterior. 



