CYTOLOGICAL INVESTIGATIONS OF COLPODA CUCULLUS

¹ From the Arnold Biological Laboratory of Brown University and the Marine Biological Laboratory, Woods Hole, Massachusetts

1. A complete description of the nuclear activity of Colpoda cucullus Muller is given for the first time.

2. In our strain the normal method of reproduction takes place within a thin cyst membrane. Usually two divisions result giving rise to four daughter organisms which break out of the cyst and repeat the process. Occasionally binary fission occurs within the cyst. Rarely quadruple division occurs without encystment, as described by Penn (1937).

3. Following each cell division there occurs a reorganizational process within the daughter macronuclei resulting in the elimination of a quantity of residual chromatin. The residual chromatin is cast into the cytoplasm where it is absorbed. Elimination of residual chromatin is regular and synchronous in each cell whether the division has occurred within a cyst or not.

4. When cultural conditions are poor resistant cysts are formed.

5. The resistant cysts are formed by the secretion of a heavy cyst membrane, the absorption of the food inclusions and the concentration of the whole protoplasmic mass.

6. Immediately following the formation of the resistant cyst membrane the macronucleus undergoes a profound reorganization during which a variable, but always a considerable amount of chromatin is budded off and cast into the cytoplasm where it is absorbed. No micronuclear activity occurs at this time.

7. The question of chromatin elimination from the macronuclei of holotrichous ciliates is discussed and the opinion expressed that this phenomenon may represent a universal principle.