STUDIES ON THE CILIATES FROM FRESH WATER MUSSELS

II. THE NUCLEI OF CONCHOPHTHIRIUS ANODONTÆ STEIN, C. CURTUS ENGL., AND C. MAGNA KIDDER, DURING BINARY FISSION

¹ From the College of the City of New York and the Marine Biological Laboratory, Woods Hole, Mass.

1. The nuclear phenomena incident to fission are described for three ciliate commensals of fresh water mussels, Conchophthirius anodont, C. curtus, and C. magna.

2. The micronuclear chromatin of C. anodont forms a granular spireme in the prophase. From this spireme form twelve distinct rod-like chromosomes. On the metaphase plate each chromosome splits longitudinally. In the early anaphase the daughter halves slip past one another and form two groups of twelve chromosomes each. The late anaphase and the telophase are quite regular, the compact daughter micronuclei forming from the twelve daughter chromosomes.

3. The macronucleus of C. anodont undergoes fission, throwing out a deeply staining ball of chromatin near the division plane. This residual chromatin disintegrates and is absorbed into the cytoplasm.

4. C. curtus and C. magna parallel C. anodont in all nuclear activity during fission. The micronuclei are, however, too small to permit the observation of minute details.

5. Several cases of abnormal divisions are reported, occurring in all three species. In these cases it would appear that the synchronization of cytoplasmic and nuclear activity had, in some manner, become disorganized.

6. A short review of the literature dealing with ciliate fission, particularly that concerning micronuclear mitosis and the extrusion of macronuclear chromatin, is given.