Sex of Parabiotic Twins of Ambystoma Maculatum (Shaw). 20

Abstract

Since Burns published his paper on “the sex of parabiotic twins in amphibia,” 1 it has been found difficult to reconcile his statements and his general conclusions with the results of other experimental studies in sex development of vertebrates. He alleged that everyone of 80 pairs of Ambystoma maculatum joined in parabiosis at the tailbud stage had developed into unisexual twins, 36 being of the female and 44 of the male sex. The absence of heterosexual combinations was said to suggest that embryomc sex differentiation is a hormone controlled reaction of the “all or none” type. Moreover, the approximate 1:1 ratio of male and female pairs was taken as an indication that there is no prepotency constantly favoring either sex, but that in genetically heterosexual pairs the first differentiating member governs also the development of its mate so as to develop into the identical sex. In contrast to this, Witschi 2 and Witschi and McCurdy 3 found in parabiotic frogs and newts a clear ratio of 1:2:1. In cases of secondarily induced sex reversal the male sex predominated. Later Burns 4 reported new experiments with Ambystoma tigrinum that gave results corresponding closely to ours. However, he still upholds the accuracy of his original statements with respect to Ambystoma maculatum. Differences of such fundamental character within one genus seemed extraordinary and since they were an obstacle to a rational interpretation of the whole body of experimental data, the authors were moved to repeat Burns' experiment with the same material—Ambystoma maculatum (Shaw), syn. A. punctatum (L) of New Haven, Connecticut. Though the investigation which was started in the spring of this year is not yet completed, it is already clear at this time that Burns must have misinterpreted his material.