1919] Rhodes: Binary Fission in Collodictyon tricilutlum Carter 221 



circumfluence (Minehin, 1912, p. 189). The food is frequently sur- 

 rounded by engulfing protoplasm of the pseudopodium before it begins 

 to sink into the vacuolated body, but the latter process always takes 

 place and at such times there may be a considerable shifting of internal 

 vacuoles. Once I noticed the rupture of several vacuoles on the engulfing 

 of a very large Pandorina morum, undoubtedly explicable by the move- 

 ments of the captured organism. Collodictyon may engulf much food, 

 almost as much as its own size and still appear very little larger. 

 France cites an instance where ten Euglena minima and Chlamydo- 

 monas filled up the interior of Collodictyon. Its normal cytoplasmic 

 vacuoles must, therefore, not only be displaced, but also ruptured 

 and the food vacuole take the place of one or more of these Then' is 

 always a slight water ring surrounding the new food vacuole, but as 

 it grows older this seems to be supplanted by a protoplasmic film 

 coming directly in contact with the substance being digested. Tests 

 with Congo red and litmus bring out these differences intra-vitam. 

 In the use of the former, the food vacuoles present, for some time 

 appear red, thus indicating alkalinity, but the small vacuoles in final 

 stage of digestion are blue, indicating acidity. Litmus did not yield 

 such good results, though the water film was shown up very well. 

 Collodictyon has been seen to be engulfed by a larger form of its own 

 species. It is not only a cannibal, but is very voracious, and almost 

 omnivorous. Peridinium, Pandorina, Euglena, Amoeba, Chlamydo- 

 monas, a ciliate (presumably Colpidium), Pediastrum, Scenedesmus, 

 Lagerheimia, Ulothrix, Chlorella, Navicula, and Gonium, have been 

 observed being ingested or in food vacuoles within the body (pi. 9, 

 figs. 19-27). 



MITOSIS 



Resting Stage 



In the normal nucleus of Collodictyon in the resting stage the 

 following organelles appear to play important roles. The nucleus is 

 surrounded by a nuclear membrane, which stains very lightly with 

 iron haematoxylin, but a dark red with acid fuchsin and safranin. 

 The shape of the nucleus is variable but typically is an ovoid flattened 

 on the posterior side or anteroposteriorly, the longitudinal axis lying 

 perpendicidar to the major axis of the cell. This nucleus is vesicular. 

 The central karyosome measures 2 to 3/x in diameter and appears 

 homogeneous with all stains except Bordeaux red, iron haematoxylin, 

 and neutral red used intra-vitam, with which it appears granular; 



