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.

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    various series should be known and taken into account in con- sidering the results. With the large numbers of eggs that were necessarily used in these studies it was quite impossible to take the time to make an accurate count of the eggs when the experi- ments were made. For the eggs of the toad, when taken from the uterus, are so closely packed together in long strings of thick jelly-like substance that they are greatly distorted in shape, and a rather careful examination with a lens would be necessary to enable one to tell the exact number of eggs in any given lot. It is possible that distinct variations in the sex ratios might be obtained when batches of eggs from different females are fertilized with sperm from different males. A control for each series of experiments was therefore considered necessary, and was obtained by fertilizing eggs from the same female with sperm from the same male in ordinary tap water. The percentage of females in this control lot was taken as the standard by which to judge whether the sex ratio had been altered by the changed environmental conditions to which the particular lot of eggs had been subjected at the time of fertilization. i. The Influence of Alcohol on the Sex Ratio of Bufo. To subject eggs to the action of solutions that would produce marked alterations in the cell structure would seem to be an easy way of ascertaining whether sex can be influenced by ex- ternal conditions acting at the time of fertilization. Unfortu- nately the unfertilized eggs of amphibians, as well as those of the different invertebrates that are extensively used for experi- mental purposes, are very sensitive to the action of various sub- stances, even when used in very dilute solutions for only short periods of time. It is therefore not possible to put the eggs of Bufo in any solution strong enough to greatly modify the cell structure without causing immediate death or inducing changes that prevent normal development. Experiments made by Morgan and Tsuda (’93) show that the eggs of the frog, and also those of the toad, can develop normally for some time if they are placed in a 2.5 per cent, solution of alcohol, although they are not able to live in a 5 per cent, solu- tion. As eggs and sperm, according to Overton (’02), are equally