The presence of many small [male] [male] and no small [female] [female] among some hundreds of specimens of P. danae suggested that this species might be protandrous. Detailed observations were made on the secondary sexual characters and on the macroscopic and microscopic structure of the gonads in shrimps of various sizes. All evidence seems to support the idea that the shrimps are essentially [male] [male] for 2 years and then undergo a change of sex.