GONOPODIAL CHARACTERISTICS PRODUCED IN THE ANAL FINS OF FEMALES OF GAMBUSIA AFFINIS AFFINIS BY TREATMENT WITH ETHINYL TESTOSTERONE

anal fins of males and of females are practically identical in structure but the fins of the two sexes become structurally divergent with the ap proach of maturity. Rays 3, 4 and 5 of the male fin undergo elonga tion and six differentiation areas arise within which characteristic hooks, spines, serrae and plates develop. In the female fin there is no marked elongation of the 3—4—5 ray complex and the differentiation areas do not arise to elaborate the morphological features peculiar to them. Regnier (1938) was able to induce the development of some of the gonopodial characteristics of the male in the anal fins of the females of Xiphophorus helleri and Lebistes reticukitus by intramuscular injections of testosterone propionate, thus proving that the genetic factors for a gonopodium are borne by the female but that, in the absence of an androgenic hormone, they are not expressed. Grobstein (1940) ob tained the same result in Platypoecilus maculatus but was able to demon strate in addition that an anal fin of an adult female produced the fea tures of the male gonopodium more exactly if that portion of the fin which gives rise to the male characteristics was cut away and allowed to regenerate during the treatment with testosterone propionate. Ever sole (1939) was able to secure the formation of atypical gonopodia in females of Lebistes reticulatus at various stages by injecting testo sterone propionate peritoneally and by adding testosterone propionate to the ration. The writer is indebted to Eversole for the information that pregneninolone (ethinyl testosterone) and other androgenic hor mones will produce a similar effect. The writer has studied in detail the normal development of the anal fins in males and females of Gambusia affinis affinis (Turner, 1941a) with particular attention directed to the origin of the marked differences