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

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Abstract
Expts. involving transfer of attached cryptoniscus larvae of this ectoparasite of the hermit crab Pagurus longicarpus from the host to the female parasite and vice versa, are discussed in relation to the problem of sex-determination in the Bopyridae. Stegophryxus seeks the definitive host as a free-swimming cryptoniscus which is sexually undifferentiated and sexually undetermined. Changes in the color pattern of the larvae following fixation furnish criteria for judging the length of time they have been subject to a particular environ- ment. Females result from cryptonisci that settle on the abdomen of the host while males result from cryptonisci that attach to the female parasite. Presumptive female larvae, if removed from the crab at an early age and transferred to the brood pouch of a female parasite become males. Failure of the converse expt. (transfer of presumptive male cryptonisci from the female parasite to the host) is attributed to exptl. difficulties. The environmental factor that determines maleness is believed to be a masculinizing substance imbibed with food from the female, but this substance does not act at a distance. These expts. are compared with those of Reverberi (1942, 1947) on Ione and the general pattern so revealed leads to the conclusion that sex-determination in bopyrids is environmental, but that details of the mechanism vary somewhat from sp. to sp.

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