The experiments described have given the following conclusions: (I) A chemical signal (pheromone) emitted by the oviparous female has an attractive effect upon the males. This signal is not emitted by the virginogeniae. (2) The signal is emitted by organs situated on the hind tibiae of the oviparous female and perceived by organs on the male antennae. (3) The substance is only emitted by the females during a certain period in their lifetime. Apparently, this is principally the condition which has been called active copulatory period (ACP). No emittance was found neither during the passive precopulatory period (PPP) nor during the passive postcopulatory period (PCP). (4) Males are capable of detecting and reacting to the signal already in the last two larval instars. (5) The males do not emit any substance affecting other males. Statistical analysis (Student's t-test) of the material has been excluded as it gave significance only in experiments where differences between the stimuli are apparent.