Horváth Géza (szerk.): A Magyar Természettudományi Múzeum évkönyve 8. (Budapest 1910)
Soós, L.: A Helix arbustorum hím csirasejtjének fejlődése
314 LH L. SOÓS to B ONNEVIE (13. 14) are split after the first maturation division, but the chromosomes of Enteroxenos are also divided earlier. The first maturation division is succeeded either immediately by the second one, or a shorter or longer resting period is intercalated between them. In the first case the formation of the second maturation spindle begins at the moment when the first spermatocytes arrives at the last period of the anaphase, and when the fibres of the first spindle are yet in full vigour. The mode of the division is seen on the Fig. 4., Pl. X., and Fig. 11., Pl. VIII. The division takes place as follows: The chromosomes in the anaphase of the first spermatocytes arrange themselves in a place the axis of which is at right angles to the axis of the spindle. Then they change their position, and order themselves in a plane which is at right angles to their former position (Pl. X., Fig. 4.). At the same time the centrosome also divides and the daughter centrosomes pass toward opposite poles. Concurrently forms the second maturation spindle the axis of which is at right angles to that of the first spindle. We can see on Fig. 4., Pl. X., that the one daughter group of chromosomes of the first spermatocytes already occupied the equatorial plate of the new second spindle, and the second group is in rearranging concurrently with the formation of the spindle, while the fibres of the first spindle have not yet disappeared. Fig. 1 1., Pl. IX., shows a later stage, the late metaphase immediately before the telophase. This figure shows a cell having two parallel spindles which have arisen in the manner described above, while the division of the cell is indicated only by a slight incision. On. Fig. 9., Pl. X., four spermatids are figured, the reciprocal position of which indicates a similar origin. At an other time, as mentioned, a resting period is intercalated between the two divisions. The duration of this period is variable. Sometimes the nucleus does not transform itself, strictly speaking, into a resting nucleus, i. e. no nuclear membrane arises, and the chromatin does not form a reticulum (Pl. X., Fig. 3.\ but the chromosomes remain separated, and soon arrange themselves in the second maturation spindle which has arisen in the mean-time. We can sometimes observe in such cells even the fibres of the first spindle which fact points to a very short resting period. The first division is, however, in most cases, succeeded by a longer resting period, when a distinct nuclear membrane arises, i. e. the nucleus becomes reconstructed. The chromatin of these cells forms larger masses connected by achromatic threads (Pl. X., Fig. 2.), in which chromatin granules are suspended. This stage is in some respects similar to the resting stage of the spermatogonia and spermatocytes, but
