The sex chromatin body and its importance for the demonstration of heterochromosomal conditions in Ornithodoros moubata (Murray, 1877).

Geigy & Wagner (1957) and Wagner-Jevseenko (1958) studied normal mitoses in squash preparations of metaphase nuclei in the argasid tick Ornithodoros moubata during the transition of the oogonia to the primary oocytes and anived at the diploid chromosome number 20. Morphologically the chromosomes could be differentiated into two main groups: three large, rod-shaped chromosomes, ca. 1· 7 p. long, and 17 small, mostly rodor coccus-shaped structures. In the male, as seen during the division of the spermatogonia, an almost analogous morphology exists; on the whole the chromosomes were only somewhat larger. The three largest chwmosomes were 3 · 1 p. in length. Neither in the female nor in the male was it possible to match the chromosomes into homologous pairs. Geigy & Wagner (1957) could not find distinctive sex chromosomes. Wagner-Jevseenko (1958), therefore, concluded that the hetero-chromosomes are most probably lacking in Ornithodoros moubata. This finding agrees with that of Sokolow (1954).