238 University of California Publications in Zoology [VOL. 19 



amoeboid, then the sulcus of Collodictyon may be regarded as a vestigial 

 character, a restricted surface area retained from a Rhizomastigina 

 type. Collodictyon would thus be closely related to the rhizopods, not 

 far removed from the ancestral type from which the latter diverged 

 from the evolving flagellates. By such an interpretation it would 

 naturally be considered an organism of a generalized or possibly a 

 primitive type. If, however, the primitive phylogenetic type be re- 

 garded as a polarized flagellate with a non-amoeboid surface, then the 

 sulcus of Collodictyon must be regarded as a highly specialized cyto- 

 stome. 



Among the specific and generic characters of Collodictyon which 

 may be called diagnostic, I find : 



1. The number of flagella is four. Carter erred in this. 



2. I find no contracting vacuole (I am loath to say that there is 

 none). Carter (1865) described but did not figure "contracting 

 vesicles;" Kent (1880-82, p. 308), with seeming authority from Carter, 

 denied that there were any; "such an open vacuolar character of the 

 parenchyma would seem to obviate the necessity for a contractile 

 vesicle, the presence of which structure Mr. Carter was unable to 

 detect." Stein (1878-83) described and figured one in the anterior 

 end near the nucleus; France (1899) with difficulty found one in the 

 anterior end and timed its pulsation at about every forty seconds; 

 Klebs (1893) found one in the posterior end in the Tetramitus he 

 described as "sulcatus." 



3. The flagella are equal in length, being as long or slightly longer 

 than the body. This possibly was the basis of Kleb's mistaken 

 identity. 



4. The sulcal region is a modified surface area and may be regarded 

 as a cytostome. The classification of Delage and Herouard (1895), 

 Lankester (1909), and Calkins (1909) involves this in their Tribe 

 Monostomatina. 



5. There is an extranuclear centrosome just at the point where the 

 rhizoplasts enter the nuclear membrane. It is, therefore, outside of, 

 but connected with, the blepharoplast. In mitosis a paradesmose is 

 formed between the dividing centrosomes. These characters establish 

 polymastigote affinities. 



6. Blepharoplast (so defined as not to include the division center) 

 consists of two basal granules embedded in a chromatoidal matrix or 

 surrounded by a granular archoplasm. The basal granules are con- 

 nected to the nucleus by faint rhizoplasts. 



