1919] Rhodes: Binary Fission in Collodictyon triciliatum Carter 241 



The possibility of Collodictyon becoming ectoparasitic upon the 

 gills or endoparasitic in the intestine is a very fertile field for specula- 

 lation and experiment. I have nearly always found Collodictyon when 

 examining preparations brushed from the gills of goldfish of the 

 aquarium. This may have been due to their normal abundance in the 

 water. In attacking dinoflagellat.es, large Euglena, and other rapid, 

 free-swimming organisms, Collodictyon may grasp the body of its 

 prey in a death clasp \vith all four flagella. At times I have seen one 

 flagellum free in such attacks. Normally, in attaching itself to the 

 substrate all four flagella are spread out radially and its body may 

 be drawn down close and tight or left suspended at a considerable 

 height. In such a state it can revolve clockwise or counter-clockwise 

 upon its major axis. We can hardly imagine Collodictyon modified 

 directly into a Costia-like animal, though the differences are not so 

 great. In Costia there are four flagella, two of which are long and 

 used for fixation, two of which are short and used for wafting food 

 to the cytostome. All four function in locomotion. In Collodictyon, 

 the four flagella occur in two pairs with separate basal granules, but 

 all are of equal length and undifferentiated in structure and function. 

 When we consider its omnivorous propensities it seems possible that 

 it could easily adapt itself to an ectoparasitic life, and possibly does so. 



Its extreme delicacy of protoplasmic texture and tendency to 

 rupture under slightly unfavorable conditions, makes it improbable 

 that it may directly become an endoparasite, even in the rectal region 

 of fishes. That it could not pass uninjured through the stomach and 

 into the intestine, would be evident to all who could observe it closely. 

 But its great variation in size with correlated reduction of cytoplasmic 

 vacuoles, and the possible modification of the sulcal region into a 

 cytostome similar to that in Trichomonas, or a cytostomal region of 

 attachment, leads me to offer Collodictyon as a possible free-living 

 ancestral type, or near relative of such at least, of these highly 

 specialized genera. 



MITOSIS 



Since the discovery of a method of cell division by Remak, the 

 evidence of mitotic phenomena has accumulated rapidly. The early 

 discussion, and late as well, centers about the universality and then 

 the very existence of amitosis as a method of cell or nuclear division. 

 To this mooted question my observations can add but little of decisive 

 value. It is evident that Collodictyon presents still another example, 



