Chromosomes in the male germ-cell of two species of dragonflies belonging to the Gomphinae (Aeschnidae) have been studies.
(1) The spermatogonium of Tachopteryx pryeri Mats. contains 17 chromosomes (Fig. 1). The diploid number, 17, is the lowest one so far reported in the dragonfly. A pair of small m-chromosomes and an unpaired X-element can be easily distinguished among them by their shape and size. The m-chromosomes of this species are characterized by their minute size. The primary spermatocyte metaphase shows nine chromosomes composed of eight autosome tetrads and an X-element (Figs. 2-3). In the first division all the chromosomes including the X are divided into equal halves (Fig. 4). In the second division the X, unlike the outsomes, does not divide but goes to one of the two poles entire (Fig. 5). Thus there are obtained two kinds of spermatids, one having the X-element (Fig. 6), the other without it (Fig. 7).
(2) In the primary spermatocyte metaphase of Gomphus hakiensis Selys 12 chromosomes are found including an X-element (Figs. 8-9). There is distinguished no conspicuously small element which can be called an m-chromosome. The X-element, as in all the cases of the dragonfly, divides equationally in the first division (Fig. 10), and runs ahead toward one pole without separation in the second division (Fig. 11), two kinds of spermatids, with and without the X, being produced (Figs. 12-13).
