Internal Factors of Sex Determination 397 



''overripe." Only a small number of them segmented. The 

 next table gives the results : — 



The excess of males is much greater in the overripe set. Hert- 

 wig concludes from these data that the overripe condition favors 

 male production, because the nucleus undergoes an increase 

 in size during the period of overripening. The improbability 

 of this assumption is manifest when we recall that when the eggs 

 have reached the uterus, the nucleus has disappeared as such, 

 and the second polar spindle has formed in the egg. In regard 

 to the results from the eggs prematurely fertiHzed, Hertwig thinks 

 that they can be accounted for by assuming that the cytoplasm 

 has not fully developed at this time; but this assumption also 

 seems improbable, since the eggs of the frog reach their full 

 growth in the autumn of the year preceding their deposition. 

 Hertwig's attempt to bring these results — as well as others 

 relating to the influence of temperature as a sex-determining 

 factor in the frog's egg — seems forced, and his general theory 

 finds little support, I think, in the outcome of his experiments. 



The 'Extrusion 0] the Polar Bodies, and the Analogous Process 

 in the Sperm-cells 



The fact that the Qgg throws off two polar bodies before it 

 begins its development has led to much ingenious speculation 

 in modern times. Amongst other views that have been suggested 

 as to the meaning of this ''maturation " process it has been urged 

 that in one or both of the polar bodies the male or the female 

 element is ejected. This view was first proposed by Minot in 

 1877, and adopted later by Balfour, 1879, ^^^ by van Beneden, 

 1883. More recently Castle has offered a more elaborate hy- 

 pothesis that rests on the same foundation. 



The discovery that most eggs extrude two polar bodies was 



