1919] Rhodes: Binary Fission in Collodictyon triciliatum Carter 235 

 To these Dobell added a fifth : 



5. Nuclei in which the achromatic division-centre lies freely in the cell, 

 whilst the chromatin is diffuse in the form of chromidia. 



In such a classification Collodictyon finds no place. Recent work of 

 Tschenzoff (1916) on Englena and of Belar (1916) on Astasia show 

 related nuclear phenomena which furnish an interesting comparison 

 with Collodictyon. These possess a " nucleolo-centrosome " (Keuten, 

 1895), the significance of which seems not to be well understood. 

 In division it presents the appearance of a centrodesmose. Collo- 

 dictyon possesses no such evident body or nucleolo-centrosome, but 

 there is evidence of an extranuclear centrosome similar to that in other 

 polymastigotes. There is a much more perfect spindle and all 

 chromatic material of the nucleus in the metaphase is located upon 

 the equatorial plate. It thus seems to have a more advanced type of 

 mitosis than do the above-mentioned Euglenoidea. With the present 

 advancement in the science of protozoology it would seem possible 

 to review the various groups of flagellates already recorded, not only 

 describing their typical vegetative, but their mitotic phenomena, and 

 to establish complete life cycles for the majority. But such is not 

 the ease. All previous investigations of Collodictyon, to use it as an 

 example, have omitted description and discussion of mitotic and 

 related phenomena. It is hoped that this knowledge has been brought 

 out in sufficient detail and accuracy to warrant future correlations 

 and comparisons, though little more than a beginning is claimed to 

 have been made. 



Because of its plastic nature and its mode of incepting food, "for 

 it does not appear to possess any oral aperture," Carter (1865, p. 289) 

 classified Collodictyon as a rhizopod. He, however, acknowledged its 

 similarities to Bodo Ehr., in its voracity especially, to Polyselmis 

 viridis Duj., and to Actinophrys eichornii in its vacuolated cyto- 

 plasm, the "cellular spaces which pervade its body." These com- 

 parisons have little significance today. 



Stein (1878), naming it Tetramitus sulcatus Stein, placed it in the 

 flagellate group and in the first family, Monadina, together with the 

 genera: Cercomonas, Monas, Goniomonas, Bodo, Phyllomitus, (Tetra- 

 mitus}, Trepomonas, Trichomonas. Hexamitus, Lophomonas, and 

 Platytheca. 



Kent (1880-81) interpreting Carter's and Stein's organisms as 

 different, put both under Order IV, Flagellata-Pantostomata ; Collo- 

 dictyon in Family XIV, Trimastigidae with Trichomonas, Dallingeria 



