1919] Rhodes: Binary Fission in Collodictyon triciliatum Carter 211 



and defense. In attacking a dinoflagellate they were observed to catch 

 their prey with all four flagella ; they then allowed themselves to be 

 pulled about until the dinoflagellate was exhausted, when it was drawn 

 back to the anterior end of the sulcus and engulfed. On another 

 occasion when Collodictyon was being drawn toward the mouth of a 

 rotifer, it spread its flagella and lodged upon the oral membrane ; at 

 other times it was enabled to guide itself to one side of the oral current. 

 While not the most conspicuous, the flagella constitute the most useful 

 organelles of this slightly differentiated unicellular organism. 



Fig. B. 1-4. Extrusion of Lagerheimia by Collodictyon, showing false pseudo- 

 podia. 5-8. Unsuccessful attempt of Collodictyon to engulf long Ulothrix fila- 

 ment. Diagrammatic. X 750. 5. Extension of protoplasmic sheath along 

 filament. 6. Contraction of protoplasmic sheath forcing the filament anteriorly, 

 pushing out the surface. This was repeated several times. 7. Retraction of 

 protoplasmic sheath. 8. Extrusion of filament. 



The sulcus is usually a smooth depression, but when Collodictyon 

 is actively searching for food, pseudopodia are extended from any or 

 all portions of the sulcal region. These may be of various types, 

 hatchet-shaped, lobose, finger-like, or filose (text fig. A, 1-5). Finger- 

 like pseudopodia from over the entire surface of the body were observed 

 (text fig. A, 6), but such are very rare. The entire sulcus at times 

 may become serrated and undulating, exceedingly amoeboid and meta- 

 bolic. The posterior end may put forth lobose pseudopodia or flow 

 around objects being engulfed (text fig. B, 1-6). The posterior cusps 



