STUDIES ON THE CILIATES FROM FRESH WATER MUSSELS II. THE NUCLEI OF CONCHOPHTHIRIUS ANODONIVE STEIN, C. CURTUS ENGL., AND C. MAGNA KIDDER, DURING BINARY FISSION GEORGE W. KIDDER (From the College of the City of New York and the Marine Biological Laboratory, U'oods Hole, Mass.) In a previous paper (Kidder, 1934) I have given a description of the general morphology, neuromotor apparatus, and vegetative nuclei of the three species of Conchophthirius to be discussed in the following pages. Mention was made of the occurrence of binary fission, and the general appearance of the metaphase spindles was figured. It is the purpose of the present paper to report the cytological details of the nuclear phenomena during division and to point out differences from and similarities to the nuclei of related forms. Relatively few of the many descriptions of ciliate division give a detailed account of the number and behavior, during binary fission, of the micronuclear chromosomes. Especially noticeable is the general lack of close observations as to the period between the metaphase and the anaphase stages with regard to the method of chromosomal division. This situation is quite obviously due to the difficulty of observation of so small a cell element and also in part to the usually short duration of this stage. "Whether ciliate chromosomes divide transversely or longi-tudinally is of great theoretical significance, as was clearly pointed out by Calkins (1930a). A great many more observations on this point are needed before we can formulate any general conclusions. Due to the large size of the micronucleus of Conchophthirius ano-dontce, the great abundance of material, and the ease gf fixing and stain-ing, I have been able to make a detailed study of the chromosomal di-vision in this species. Although the other two species studied, C. ciirtus and C. inagna, were very plentiful, their micronuclei are so small, as pointed out before (Kidder, 1934), that I was unable to observe the chromosomes clearly and so could not be sure of the exact method of chromosomal division. In all three species the changes occurring in the macronuclei during fission could be followed with ease. The material used in this study was obtained from the same sources as those previously reported (Kidder, 1934). The preparations were 286
STUDIES ON THE CILIATES FROM FRESH WATER MUSSELS: II. THE NUCLEI OF CONCHOPHTHIRIUS ANODONTAe STEIN, C. CURTUS ENGL., AND C. MAGNA KIDDER, DURING BINARY FISSION
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