68 



THE AM ERIC AX XATCUAUsT 



[Vol. XLII 



observations — those of Born — seemed to indicate that the food 

 given to the young tadpoles determined the sex of the frog. 

 Yung also obtained about 70 per cent, of females when his 

 tadpoles were well fed. Balbiani and Hennegny have stated 



of Miss King have shown clearly for the toad that the nutrition 

 of the tadpole has no influence on the sex of the adult. De- 

 spite the fact that these recent results go far towards showing 

 that sex is not determined or even altered by food relations, a 

 curious disproportion of the sexes in frogs has been noted by 

 several observers. The recent valuable experiments of Richard 

 Hertwig do not, in the opinion of the reviewer, bear out the 

 interpretation that Hertwig has placed upon them. Neverthe- 

 less, his methods u-ive promise, if further extended, of throwing 

 light on the problem. 



In Hertwig 's first contribution to the subject published in 

 1906 he suggested that sex is determined by the condition of 

 ripeness of the egg at the moment of fertilization. This view 



ratio of nucleus to cell-plasm of the egg at different periods of 

 its maturation can hardly be looked upon favorably, since in the 

 frog's egg the nucleus as such has already disappeared when the 

 egg leaves the ovary. The chromosomes are thereafter arranged 

 on the equatorial plate of the first polar spindle. It is, how- 

 ever, during this period that the degree of ripening is supposed 

 to determine the sex of the egg. However unsatisfactory this 

 specific suggestion of Hertwig may now appeal-, the possibility 

 must still be granted that in some way the degree of maturity 

 of the egg may have an influence on sex-determination. Hert- 



