A COMPARATIVE STUDY OF THE CHROMOSOMES OF LACHNOSTERNA (COLEOPTERA)

¹ Department of Biology, Princeton University.

1. The diploid chromosome groups of four species of Lachnosterna, namely delata, fusca, gracilis and tristis, as well as Pelidonota punctata and Cotalpa lanigera, show twenty chromosomes, one pair of which is composed of two unequal elements (sex chromosomes).

2. There are no essential differences in the form and arrangement of the chromosomes in the species studied.

3. The growth period of the spermatocytes is marked by the appearance of delicate leptotene threads which are derived from the chromosomes of the last spermatogonial division. These threads become polarized and there is evidence that they are arranged in pairs parasynaptically.

4. There is a definite contraction stage which does not seem to be caused by fixation, but is a normally occurring phase in the growth period.

5. The sex chromosomes persist through the entire growth-period in the form of definite compact bodies, sometimes being contained within chromosomal vesicles. The unequal sex elements separate in the first maturation division and divide equationally in the second maturation division.

6. There are five atelomitic tetrads in the first maturation division and five telomitic tetrads (including the sex pair).

7. Cyst formation in the testis begins by the rapid division of a single primary spermatogonium, so that all the cells within any particular cyst are the descendants of a single cell. The visible polarity of the cells seems to be established at the time of cyst formation.