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Journal of Experimental Biology 25,227-236 (1948)
Published by Company of Biologists 1948

Vapour Pressure Changes in the Frog's Egg at Fertilization

L. E. R. PICKEN ¹ and LORD ROTHSCHILD ¹

¹ Department of Zoology, University of Cambridge

1. The vapour pressure of unfertilized and fertilized frogs' eggs has been measured by the differential thermal method.

2. The following results were obtained; they are expressed as decimal fractions of the vapour pressure of a 1% aqueous solution of sodium chloride:

Coelomic eggs (eggs free in the body cavity, before entering the oviducts) 1.06

Uterine eggs (eggs in the distal end of the oviducts) 0.99

Unfertilized eggs, 30 min. after immersion in tap water 0.91

Inseminated eggs, 30 min. after immersion in tap water 0.84

Unfertilized eggs, 180 min. after immersion in tap water 0.67

Fertilized eggs, 180 min. after immersion in tap water 0.64

3. These results are in serious disagreement with those of Backmann & Runnström (1912) and Backmann & Sundberg (1912), but in general agreement with those of Krogh et al. (1938).

4. It is concluded that while there is probably a slight difference between the vapour pressure of fertilized eggs in tap water half an hour after fertilization, and of unfertilized eggs half an hour after transfer to tap water, the difference is negligible after 3 hr. The initial difference may be due to a more rapid interchange between egg and environment in fertilized eggs.

5. In the case of unfertilized eggs, the effect of transfer to a hypotonic medium may be interpreted as an abortive response to a parthenogenetic stimulus.