THE CELLULAR BASIS 149 



Pearl and Parshley in the case of cattle, where 

 delayed fertilization of the egg leads to a great 

 preponderance of males. Hertwig attempts 

 to explain his extremely interesting and im- 

 portant observations as due to the relative size 

 of nucleus and cytoplasm of the egg; but in 

 general this nucleus-plasma ratio may vary 

 greatly irrespective of sex and there is no 

 clear evidence that it is a cause of sex 

 determination. 



Miss King, also working on toad's eggs, has 

 increased the proportion of females by slightly 

 drying the eggs or by withdrawing water from 

 them by placing them in solutions of salts, 

 acids, sugar, etc., but the manner in which 

 drying increases the proportion of females is 

 wholly unknown. 



Extensive statistics show that in many ani- 

 mals including man more males are born than 

 females whereas according to the chromosome 

 theory of sex determination as many female- 

 producing spermatozoa are formed as male- 

 producing ones. It is possible to explain such 

 departure from the 1 : 1 ratio of males and fe- 

 males in conformity with the chromosome 



