I. Sex dimorphism, in agreement with the normal karyotype, was shown to
exist in interphase nuclei of the argasid tick Ornithodoros savignyi.
2. Sex-chromatin bodies were suitably demonstrated only in nuclei of the rectal
sac. Other tissues proved to be completely unsuitable.
3. An adapted method, giving excellent differential staining of the sex-chromatin
bodies, is described.