30 



GENERAL ORGANIZATION OF THE PROTOZOA 



tatives of the flagellated and ciliated protozoa, and a characteristic 

 form is found in Euglena viridis and its allies (Fig. 10). Here a 

 definite intranuclear body is surrounded by chromatin granules, and 

 when the cell is ready to divide, this division centre, like a centrosome, 

 divides first and the chromatin elements are separated into two equal 

 groups, each half following one of the centres. In this case, and in some 

 of the infusoria (e. g., Paramecium aurelia [cavdatumj) the division 

 centre seems to be formed from a specific substance, and it appears 

 to be a permanent body in the cell, retaining its individuality from 

 generation to generation. 



Fig. 10 



Mitosis in Euglena. (From Wilson after Keuten.) A, preparing for division; the nucleus 

 contains a division centre surrounded by chromatin granules; B, formation of an intranuclear 

 "central spindle;" C, later anaphase, and D, telophase stage. 



Much more enlightening, however, are the conditions in the heliozoa. 

 Here, in many cases, there is a central granule in the geometrical 

 centre of the cell, which was early noted by Grenacher ('69) and 

 Schultze and called by the former the "Centralkorn." The axial 

 filaments of the pseudopodia centre in this granule, which divides like 

 a centrosome prior to division of the cell, while the axial filaments 

 radiate out on all sides like the astral fibers of a mitotic figure. Biit- 

 schli ('92) was the first to compare this body with a centrosome, and 

 the view was quickly accepted by cytologists, while the most complete 



