SPIREME KARYODIERESIS: A NEW TYPE OF REDUCTIONAL DIVISION

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Abstract
Spireme karyodieresis is the name proposed for a type of reductional division found as the first step, of treptional nature, in the differentiation of stem cells in the ovotestis of snails towards sperm nurse cells. The same type is likely to occur in other cases of somatic reduction. Reduction is accomplished by the chromosomes arranging themselves into 2 groups, each group forming a helical chain with the chromosomes abutting each other. Each of these chains, which may be more or less coiled according to the species, may be considered to be a spireme. The nature of the process of catenation or chain formation by fusion of abutting telomeres is discussed. After 2 spiremes are formed, a bud appears into which the extreme of 1 of the spiremes is directed. In the next step the transfer of this spireme to the bud, which grows and usually bends in relation to the body of the mother-cell, is achieved. The nuclear membrane is maintained intact until the end of the division, which produces 2 cells each with a volume about 1/2 that of the mother cell. Each spireme comprises a complete or nearly complete haploid set of chromosomes, separation of genomes being apparent in mitoses of other cells in the ovotestis. This type of division is compared with other reductional divisions and the processes of genome separation and catenation are discussed in relation to reduction in chromosome number in general.

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