KARYOMERE FORMATION IN CLEAVING EGGS OF TETRODONTOPHORA-BIELANENSIS (COLLEMBOLA)

The term ''karyomere'' designates a particular kind of organization of the telophase nucleus, in which each individual chromosome is surroun ded by a typical nuclear envelope, thus representing a small nuclear s tructure. In T. bielanensis they are formed during first prophase and subsequently change into chromosomes making a metaphase plate. Each me taphase chromosome is completely enclosed by a double envelope, simila r to a nuclear one but devoid of nuclear pores. The only place on the chromosome where the envelope is not complete is the region of the kin etochore. Anaphase starts with the division of the chromosomes into ch romatids and subsequent decondensation of the latter. During anaphase, the process of decondensation of the chromatids starts at the leading ends of each chromatid and hence, they acquire a tennis racket-like a ppearance. As a result, on the spindle poles two groups of the chromos ome vesicles or karyomeres are gathered. Each karyomere has the appear ance of a typical nucleus enclosed by a double envelope pierced by nuc lear pores, filled with nucleoplasm containing patches of chromatin. I t is suggested that karyomeres are formed only in species with a large amount of chromatin in their nuclei.