SHORTER ARTICLES AND DISCUSSION 



IS THE CHANGE IN THE SEX-RATIO OF THE FROG. 

 THAT IS AFFECTED BY EXTERNAL AGENTS, 

 DUE TO PARTIAL FERTILIZATION ? 

 In a review in this journal (XLV, 1911) of certain experi- 

 ments by Kuschakewitsch 1 on frogs' eggs in which by delaying 

 fertilization for 89 hours he obtained 100 per cent, of males, 

 I pointed out that unless more than half of the eggs were fer- 

 tilized the interpretation of the 100 per cent, ratio might be mis- 

 leading. For should the delay act more injuriously on one kind 

 of egg than on the other, assuming two kinds to exist, the result 

 might mean only selective destruction by an external agent 

 rather than a change in sex of the eggs. I found no explicit 

 statement in the section of Kuschakewitsch 's paper dealing with 

 these results to show whether or not all of the eggs had been 

 fertilized, but in a recent rejoinder 2 to my review Kuschake- 

 witsch points out that he had stated that practically all of the 

 eggs ("so gut wie alle Eier") were fertilized and developed. 

 This information is given in an appendix which I had overlooked. 

 His statement completely sets aside the possibility of the sug- 

 gestions that I made, but leaves the explanation of his results as 

 obscure as before. 



The details of the principal experiment and of some of the 

 others are of interest. A pair of copulating frogs were caught 

 at 12:00, midday, May 31. The female began to lay at once. 

 At 6:00 p.m. the male was removed. On the 4th of June at 

 8 :00 p.m. the eggs that had remained in the uterus of the female 

 were artificially fertilized. They are recorded as 89 hours old 

 at this time. Practically all segmented, and only 5 died at the 

 gastrulation stage. From this lot, 434 eggs hatched. Only 12 

 deaths occurred later. Three hundred of the tad-poles were 

 examined at the time of or after metamorphosis. Of these, 299 

 were males, and one was a bilateral hermaphrodite. 



There can be little doubt, therefore, that, in some way, delay in 

 fertilization has caused practically all the eggs to produce males ; 

 and the evidence is the clearer since the eggs fresh laid, fertil- 

 ized by the same male, produced 55 males and 53 females. 



It may seem futile, therefore, to attempt to explain this result 

 m any other way than as the result of the action of the environ- 

 ment on the sex of the egg. But how lias the environment 



1 Festschrift, E. Hertwig, Bd. II, 1910. 



'Anatom. Anzeiger, 1911. 



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