1919] Rhodes: Binary Fission in Collodictyon triciliatum Carter 237 



orders Rhizomastigina and Binucleata (Rhizomastigina, Protomona- 

 dina, Binucleata, Chromomonadina, Euglenoidea, Phytomonadina). 

 This is the system adopted by Hartmann. 



Calkins (1909) and Lankester (1909), as did Delage and Herouard 

 (1895), put Collodictyon in the tribe or subtribe Monostomatina, 

 organisms with mouth opening at the base of the group of from four 

 to six flagella, as contrasted with the Astomea, which have no special 

 mouth openings. The sulcal region of Collodictyon may indeed be 

 regarded as a cytostome. In this structure, however, we have an 

 extension of the cytostome as a metabolic surface. Its pseudopodia 

 mark it as a generalized rather than a specialized type. Collodictyon 

 may thus be regarded as comparable with organisms like Mastig amoeba 

 Schultze, Cercomonas crassicauda Dujardin, and Tetramitus or Tricho- 

 monas. Regarding the above classification, therefore, the validity of 

 the tribes Astomea and Monostomatina is lessened or Collodictyon 

 must be regarded as an intermediate type. 



Neither Doflein in his Lehrbuch (1911) nor Minchin in his Intro- 

 troduction to Protozoology (1912) classify Collodictyon. Senn, Klebs, 

 Doflein, and Minchin, however, all accept the Order Polymastigina, 

 into which Collodictyon naturally falls. Klebs and Doflein contrast 

 this with Protomonadina, Minchin with Pantastomina and Protomona- 

 dina, Senn with Pantastomatineae and Distomatineae. These distinc- 

 tions by various authors are not so much opposed to one another as it 

 at first seems. All accept the number of flagella as of determining 

 value. It is very desirable to have no all-inclusive taxonomical groups 

 such as the older Monadina. At the same time artificial distinctions 

 do not tend to clarify the situation. Hartmann was evidently actuated 

 by such a feeling when he combined the Polymastigina with the Pro- 

 tomonadina. Collodictyon emphasizes the difficulties arising in estab- 

 lishing the distinctness of the groups Pantostomatina, Protomonadina, 

 Distomatineae and Polymastigina, especially when the nuclear 

 phenomena are considered. 



As to the location of the mouth, Collodictyon seems to have all of 

 its body somewhat metabolic, the anterior end alone being compara- 

 tively constant in shape, but the function of ingesting food is localized 

 in the sulcus, about one-fourth of the surface of the organism, assisted 

 materially by the posterior part of the body. Thus, in this feature, 

 Collodictyon seems to lie midway between the Pantostomatina and 

 the Protomonadina or Polymastigina. If the primitive phylogenetic 

 type be regarded as a polarized flagellate, with a surface entirely 



