イソガニ Hemigrapsus sanguineus (de HAAN)の X-Y 染色體

抄録

The chromosomes of Hemigrapsus sanguineus (de HAAN), a species of the shore-crab (Varuninae, Grapsidae), are described in the present paper. The diploid number of chromosomes is 128, as determined in spermatogonia (Figs. 1-3), while the haploid number is 64 as counted in both the primary and secondary spermatocytes (Figs. 4-9, primary spermatocyte; Figs. 16-18, secondary spermatocyte). Sex-chromosomes of X-Y type are found in the primary spermatocyte division (Figs. 10-15). They invariably take the central position of the metaphase plate, and segregate earlier than autosomes. The relative magnitude existing between them seems to be constant, the small one (Y) being approximately one third the size of the large one (X). It was quite difficult, however, to distinguish these two particular chromosomes among the chromosomes of the spermatogonium or of the secondary spermatocyte. In respect to the constitution and behavior of the sex-chromosomes the present species shows a close resemblance to Plagusia dentipes and Eriocheir japonicus, previously recorded by the present author (cf. NIIYAMA 1937), in parallel to their taxonomical relationships.