EXPERIMENTS ON THE DETERMINATION AND DIFFERENTIATION OF SEX IN THE BOPYRID STEGOPHRYXUS HYPTIUS THOMPSON

¹ The Catholic University of America, Washington, D. C., and the Marine Biological Laboratory, Woods Hole, Mass.

Stegophryxus hyptius Thompson, an ectoparasite on the abdomen of the hermit crab Pagurus longicarpus Say, seeks the definitive host as a cryptoniscus larva.

The free-swimming cryptonisci are sexually undifferentiated and sexually undetermined. Differentiation follows fixation and is dependent on environmental factors. These conclusions are justified on the basis of the following observations and experiments.

1. Cryptonisci that settle directly on the host develop into females; those that attach to a female bopyrid develop into males.

2. Changes in the color pattern of the cryptonisci following fixation furnish criteria for judging the length of time they have been subjected to a particular environment.

3. Histological examination of the cryptoniscus shows that the gonads are not yet present as recognizable structures.

4. Presumptive female cryptonisci, if removed from the host at an early age and transferred to the brood pouch of a female Stegophryxus, will transform into males.

5. The failure of the converse experiment involving transfer of presumptive male cryptonisci from the female parasite to the host can definitely be laid to experimental difficulties.

6. The factor that determines maleness is a masculinizing substance imbibed with food from the female, but this substance does not act at a distance.

7. Attachment of supernumerary females as well as excess differentiating males is terminated sooner or later so that a particular crab is host to only a single adult female paired with one functional male.