FLAGELLATED PROTOZOA 



55 



Euglena and its allies which may make their food by the plant 

 method. 



We are ignorant of the finer processes of assimilation in Chilo- 

 monas but are justified in assuming that it differs in no essential 

 respect from the processes in Amoeba after the proteid food 

 materials are dissolved. As there are no solids the cell contains 

 no undigested food matters and there is no defecation. Urea, 

 however, is undoubtedly formed since the organism is constantly 

 doing work and this is probably excreted by means of the con- 

 tractile vacuole, although it may also pass out by exosmosis 

 as must be the case in those proto- 

 zoa in which no contractile vacuole 

 can be found. 



Chilomonas may frequently be 

 seen in pairs swimming along side by 

 side; these are sister cells not yet 

 fully divided and they have origin- 

 ated by the longitudinal division of 

 the cell. Reproduction thus is of 

 the simplest type the nucleus always 

 dividing first, then the cell body, 

 while new flagella are formed as out- 

 growths. It is not known how these 

 originate ' in Chilomonas but from 

 analogy with other forms of flagellates where the process is 

 known two of the four at least must be new growths, in some 

 cases the old flagella are withdrawn and new ones are formed; 

 in other cases one of the two flagella goes to each daughter cell. 



The processes of feeding, growing and dividing continue for 

 days before other activities occur. Indeed for Chilomonas so 

 far as known they may continue indefinitely, but from analogy 

 wi:h other forms of Mastigophora where the full life history is 

 known, these ordinary vegetative processes are sooner or later 

 replaced by processes involving a simple kind of fertilization 

 or sexual union. In Copromonas, for example, two similar 

 cells after a long period of divisions, meet and fuse, the flagellum 

 of one of them is discarded while that of the other is used as a 



FIG. 23. Synura uvella, a 

 colony of flagellated proto- 

 zoa in which the individuals 

 are attached at a common 

 center. 



