SEX REVERSALS 259 



sideration is whether external or internal conditions may 

 affect the progonad of the prospective female in such a 

 way that it produces later functional sperm-cells. "Wit- 

 schi's evidence is in favor of such a transformation in 

 those races that are indifferent. 



In the following table (Table III) Witschi has brought 

 together the sex ratios reported by different observers 

 from different parts of Germany and Switzerland. In the 

 right-hand column the per cent of females is given; 50 

 per cent means a 1 to 1 ratio. It will be seen that in the 

 first two groups (Group I and II) the sex ratio is ap- 

 proximately 1 to 1, while in the last three groups (III, 

 IV, V) the proportion of females is higher, culminating 

 in those regions where all the individuals from a pair 

 may be females (100 per cent). These belong to the indif- 

 ferent races. 



The most important facts discovered by Witschi relate 

 to the inheritance of these differences shown by the dif- 

 ferentiated and undifferentiated races. He made the fol- 

 lowing crosses between females and males of the differ- 

 ent races. 



(1) 9 undif.by $ differ.=69 undif. 9 + 545 

 (2)9 dif. by S undif. =34 9 + 52 S 



In (1) the daughters were all undifferentiated; in (2) the 

 daughters differentiated early. He draws the conclusion 

 that the eggs of a differentiated race are more strongly 

 female-determining than the eggs of an undifferentiated 

 race. 



In another experiment he crossed undifferentiated 

 races whose " female determining power" (Kraft) was 

 greater or less, and concluded that weak eggs by strong 

 determining sperm gave the same result as strong eggs 

 by weak sperm. ' l Eggs and female determining sperm of 

 the same type have the same genetic constitution. ' ' 



