1919] Rhodes: Binary Fission in Collodictyon tricilidtum Carter 219 



granules. There is evidence in vegetative stages for a faint rhizoplast, 

 probably two strands, connecting the blepharoplast to the nucleus, and 

 at times such strands can easily be observed (pi. 8, fig. 13). In 

 division, thickened striations and fibers connecting the blepharoplast 

 and nucleus are more evident than at other times (pi. 11, figs. 40, 44). 

 These no doubt are rightly interpreted as dividing rhizoplasts. 



Normally Collodictyon is pelagic, floating near the surface of the 

 water in the aquarium, but at all times of the day and at all tempera- 

 tures tested and under all conditions of light and darkness some have 

 been found scattered throughout the aquarium. In a free drop of 

 water on a slide they tend to stratify near the substrate, but in a 

 hanging drop they swim about throughout the drop, only occasionally 

 accumulating near the slide. In the aquarium they rest both in the 

 direct sunlight and also in shaded portions; but there is a marked 

 tendency to gather nearest the source of light. When there are 

 abundant algae floating on the surface of the aquarium, they can be 

 found at or just beneath the surface and then there is a region of 

 scant distribution below which they tend to accumulate in greatest 

 abundance. This may be on account of a superabundance of oxygen 

 or to too great heat at the surface, due to the absorption of heat by 

 the algae and the surface reflection. 



As to the association of Collodictyon with water pollution and pools 

 in which decay has been or is progressing rapidly, I am less positive 

 in my convictions than France (1899) seemed in his conclusions. My 

 own observations have been that Collodictyon can not live where there 

 is a great amount of decay. They are holozoic, however (with the 

 possible exception of times when there is a symbiotic association with 

 Chlorella), and live on Protozoa and algae w r hich are associated with 

 decay. Their own life seems far removed from saprozoic nutrition 

 and I find little in the rate of multiplication that tends to confirm 

 such a supposition or conclusion. As to the fact that they were found 

 in pools where disintegration was rapidly increasing or at a maximum, 

 I am not in a position to question except from cultural experiments, 

 in which other factors might have played a determining part; but I 

 urge this same factor, unknown as it is, in explanation of France's 

 observation. France's argument that Euglena is its chief and only 



