Horváth Géza (szerk.): A Magyar Természettudományi Múzeum évkönyve 8. (Budapest 1910)

Soós, L.: A Helix arbustorum hím csirasejtjének fejlődése

SPJ^MIOGENESIS OF HELIX ARBUSTORUM. 329 period preceding the division. So it is intelligible that we find chromosomes twice during the development of the spermatocytes : they form themselves in synapsis, because the cell prepares to division, but they disappear in the next stage because division does not take place, and reappear again when the cell prepares for the second time to division, and then retain their individuality, because the division now really takes place. 5. The heterochromosomes. Heterochromosomes, as is well known, are characteristic of the germ-cells of the Tracheata. Besides this group only one animal is known which certainly has heterochromosomes, i. e. Helix nemoralis, from which they have been described by ZIEGLER (130). The second case is that of H. arbustorum. The heterochromosomes are, as a rule, well distinguishable from the ordinary chromosomes during the development of the spermatogonia and spermatocytes. It is otherwise in H. arbustorum, therefore my observations referring to them are fairly defective. I have had the opportunity of observing them only in the first maturation spindle and in the phase immediately preceding the formation of the spindle. In the latter mentioned phase a spherical chromosome of smaller size is to be found among the ordinary ones (Pl. VIII., Fig. 1). This chromosome divides during the first maturation division into two parts. The daughter chromosomes lie symmetrically in the spindle (Pl. IX., Figs. 6., S.) and pass into different daughter cells. They are also regularly spherical in shape, and ar^ considerably smaller than the ordinary chromosomes. I have not had the opportunity of observing them during the second maturation division with any certainty, though I have found even during this division chromosomes smaller than the others, but they were never in such a characteristic position as to make it possible to determine whether they were heterochromosomes, or parts of ordinary chromosomes cut away. Nor have I had the opportunity of finding them in the spermatogonia. Upon the base of these defective obse nations it is undeterminable to which group of heterochromosomes they belong. Their characteristically small size would perhaps point to their belonging to the m-cliromosomes of WILSON. Naturally, it is also not quite certain that they belong to the diplosomes at all, but it may be considered probable, because Helix nemoralis has diplosomes, and according to the researches, it can be regarded as a rule that species belonging to the same systematical category have the same kind of heterochromosomes.