Studies on sex-determination in amphibians. IV. The effects of external factors, acting before or during the time of fertilization, on the sex ratio of Bufo lentiginosus / Helen Dean King.

  • King, Helen Dean, 1869-1955.
Date:
1910
Catalogue details

Licence: In copyright

Credit: Studies on sex-determination in amphibians. IV. The effects of external factors, acting before or during the time of fertilization, on the sex ratio of Bufo lentiginosus / Helen Dean King. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    8/34 (page 210)
    from eggs that were fertilized in the stronger solutions; but the deviations of these percentages from that of the control are much too small to be considered as significant, particularly as the lowest proportion of females occurs in the lot in which the eggs has been fertilized in i per cent, alcohol and not in the lot where fertilization of the eggs took place in 2 per cent, alcohol. The relatively high percentage of females (54.23) that is found where the eggs had been fertilized in .5 per cent, alcohol is quite within the limits of normal variations in the sex ratio of Bufo. For previous studies in which the sex of nearly 10,000 young toads was ascertained (King, ’07, ’09, To) show that in any large lot of individuals there is a slight excess of females, as a rule, the proportion of females varying from 51 to 56 per cent. It is evident from the sex ratios obtained in this series of experiments that alcohol, in the strengths used and for the time it acted, has no influence on the determination of sex in Bufo. The growth of the tadpoles that developed from the eggs that were fertilized in 2 per cent, alcohol was greatly retarded. This was not apparent during the first month after the experiment was made, but became very noticeable later. At the time of metamorphosis the majority of these tadpoles had a body length of only 7-8 mm., although the body length of tadpoles of Bufo at this period is normally 11-14 mm. During early development the mortality among these individuals was comparatively slight, being not more than 10 per cent. At the approach of meta- morphosis the tadpoles, especially the smaller ones, began dying in great numbers; and during the last week of June over fifty of them died from no apparent cause. In no other series ol experiments was the mortality among mature tadpoles anywhere near as great as in this case. Alcohol, therefore, although acting for only a short time at the fertilization period in but a 2 per cent, solution, must have so affected many of the tadpoles that they were rendered incapable of undergoing metamorphosis. All of the tadpoles in this lot were normal as far as could be determined without a microscopic examination of the various organs. None of them showed defects in the central nervous system comparable to those that Stockard (’09, To) has found can be induced in embryos of fundulus by subjecting the fertilized egg to the action