Abstract
The chromosomes of Thereuonema hilgendorfi Verhoeff. a species of the Chilopoda, were investigated in male and female germ cells. The results are summarized as follows:
1) The number of chromosomes was determined for the male to be 36 in the spermatogonial division (Figs. 1-5) and 18 in the primary and secondary spermatocyte divisions respectively (Figs. 7-18). The diploid number of chromosomes in the female was given as 36 from the observation of the oogonial division (Fig. 6).
2) The chromosome complement of the male consists of 17 autosomal pairs and an XY pair of unequal size (Fig. 5). Every of the autosomal elements assume a small spheroidal form and they vary slightly in size. The X and Y elements are enormously huge in magnitude. The X is composed of three segments and the Y shows two segments. They take always the central position in the spermatogonial metaphase and are very remarkable on account of their prominently large size.
3) In meiosis the X and Y constitute the X-Y complex after conjugation (Figs. 7-10). Noticeable is the fact that the X-Y complex always splits longitudinally and segregates in an equational manner in the first division (Figs. 11-13).
4) As the result of the equational separation of the X-Y complex, every of the secondary spermatocytes produced contains the X-Y complex in a dyad nature (Figs. 14-15). In the second division the X separates from the Y (Figs. 16, 18). Thus the post reductional separation of the sex chromosomes was established.
5) Considered from the behaviour of the chromosomes in the process of separation, the chromosomes of the present species, either the autosomal elements or the sex chromosomes, seem to carry the diffuse kinetochore as described in the Hemiptera by Schrader (1947).
