PROTOZOA 



83 



sion thus results in a reorganization of the protoplasm whereby 

 the motile organs are maintained in a proper proportion to the 



tr. 



m 



a.v. 



est. 



tr. 



e.tr. 



J^m^m^ ^ww^4 



Fig. 48— ALL REPRODUCTION IN THE LONG RUN IS CELL DIVJSION 



Paramecium caudatum was caught while dividing, killed, embedded in paraffine and sectioned. 

 Macronucleus, M, and micronucleus, m, are both drawn out but not quite divided; tr., tricho- 

 cysts, some of which are exploded; g.v., gastric vacuole filled with bacteria in process of diges- 

 tion; e.tr., extruded trichocyst; est., connecting strand 



From a drawing by the author 



Magnification, 500 



size of the young individuals (Fig. 49). In many cases such 

 reorganization is accompanied by profound changes in the ma- 

 cronucleus. Uroleptus mobilis, for example, has eight macro- 

 nuclei, each of which discards about one-third of its substance 



Fig. 49— EUPLOTES PATELLA IN 

 DIVISION 



Cell division is a complicated phenomenon. 

 All of the essential structures of the cell 

 divide; the motile organs are resorbed, and 

 formed anew in smaller size, one set for 

 each daughter cell. The photograph shows 

 an end stage of division with the two 

 parts of the macronucleus, M M, still con- 

 nected. The micronucleus m has divided 



From a photomicrograph by the author 

 Magnification, 340 



into the cell body whereby a new supply of complex nucleo-pro- 

 teins is provided for activities in the cytoplasm (Fig. 18, page 

 37). The remaining portions of the old macronuclei then fuse 

 to form a single nucleus, which, with the old micronuclei, now 

 divides (Fig. 50) . Thus, cell division, in addition to the function 



