The development of the larval stages of Ophiotaenia gracilis Jones, Cheng and Gillespie, 1958, was experimentally demonstrated to occur in the copepod Eucyclops agilis. Eggs were recovered from worms found in naturally infected bullfrogs in Colorado. This is the first report of this parasite in Colorado.

Twenty-four hours after ingestion of the embryonated egg, procercoids were seen in the hemocoel of the copepod. Calcareous bodies appeared 9 days after infection. The larvae developed a cercomer by the 13th day of infection and lost it on the 16th day. Measurements and illustrations are given for the developmental stages.