214 HELEN DEAN KING. 



Of the many^ investigators who maintain that sex is already 

 determined in the ovary, only von Seligson and Dawson ('09) 

 have advocated the view that the right ovary produces male 

 eggs exclusively and that eggs which develop into females must 

 be derived from the left ovary. Von Seligson believes that only 

 the spermatozoa from the right testicle are able to fertilize 

 male eggs, and, conversely, that eggs from the left ovary must 

 be fertilized by spermatozoa from the left testicle. This, of 

 course, is selective fertilization for which at present there is but 

 little evidence. Dawson is of the opinion that the spermatozoan 

 takes no part whatever in determining sex. All of the eggs that 

 were used in the experiments described above were taken from 

 the right uterus of the same female. They should, therefore, ac- 

 cording to Dawson, have produced a great preponderance of males. 

 On the theory advocated by von Seligson two of the lots should 

 have produced a great excess of males; and, unless we assume a 

 struggle for existence between the sex-determining factors in 

 the egg and those in the sperm with a final dominance of one sex 

 or the other, it is difficult to see how the tadpole in the remaining 

 two lots could have any sex at all. 



I have not suggested the possibility that in any of these lots 

 the individuals would be exclusively males according to the views 

 of von Seligson and of Dawson, since it is very probable that 

 the right uterus of the toad, and also that of the frog, contains 

 eggs from the left as well as from the right ovary. The eggs of 

 these amphibians break through the w r alls of the ovary shortly 

 after the time that the germinal vesicle has disappeared prepara- 

 tory to the formation of the first polar spindle, and they come to 

 lie freely in the body cavity from whence they pass through the 

 oviducts into the uteri. It is very probable that all of the mature 

 eggs are expelled from both ovaries at the same time; and it is 

 not at all unlikely that some of the eggs originating in the left 

 ovary may pass into the right oviduct and vice versa. Pre- 

 sumably, however, the great majority of eggs from the right ovary 

 pass into the right uterus as, owing to the enormous numbers 

 of eggs that are produced, it does not seem possible that many of 

 the eggs can be moved from one part of the body cavity to the 

 other. The results of this series of experiments, which confirm 



