AUTOSOMAL ELIMINATION AND PREFERENTIAL SEGREGATION IN THE HARLEQUIN LOBE OF CERTAIN DISCOCEPHALINI (HEMIPTERA)

¹ Department of Zoology, Columbia University

1. In the testes of four species of the pentatomid tribe Discocephalini, the fifth lobe always shows a special type of meiosis.

2. There is no pairing in this lobe.

3. Just prior to metaphase I all the autosomes aggregate in one clump. The sex chromosomes behave quite normally through both meiotic divisions.

4. In the first division the X and Y divide equationally as in normal cells. One large autosome becomes dissociated from the aggregate and reaches the pole opposite to that attained by the rest of the aggregate.

5. A large and a small second spermatocyte result from this first division. In the small one, the single autosome goes to the same pole as the X in the great majority of second divisions.

6. In the division of the larger second spermatocyte, the aggregate is irregularly pulled into two groups.

7. Four main types of spermatids result: X + variable number of autosomes; Y + variable number of autosomes; X + one large autosome; Y. The last two types probably never reach the mature sperm stage.

8. It is pointed out that so firmly established a feature as this seemingly wasteful development in the fith or "harlequin" lobe must have some compensatory advantage, and its cytological and evolutionary significance are discussed.