478 HEREDITY AND SEX 



sex-differentiation as in the case of the hive-bee, where the 

 fertilised ova become queens and workers and the unfertilised 

 ova drones, (c) Or it may (theoretically) occur after fertilisation 

 at some stage in development epigamic sex-differentiation. 

 But the examples of this that used to be cited have given way 

 before criticism, and no convincing case is at present known. 



Here we may refer to Prof. E. B. Wilson's proposal to draw 

 a distinction between sexual predetermination and sexual pre- 

 destination. " The definitive determination of maleness or 

 femaleriess only occurs when all the factors necessary to their 

 production have been brought together. This may be effected 

 before fertilisation (' progamic determination ' of Haecker), but 

 may also first ensue upon union of the gametes (' syngamic deter- 

 mination '). Thus one may suppose that all the sexual eggs 

 of a queen-bee and of Maupas' Hydatina are predestined towards 

 maleness, but this is reversed by fertilisation when determination 



3. Different Ways of Attacking the Problem 



The problem of the determination of sex has been attacked 

 scientifically along three distinct lines, which are complementary, 

 not opposed. In some cases there has been a combination of two 

 methods. 



Statistical. Some conclusions as to the determination of the 

 sex of the offspring have been based on statistics, e.g. of the 

 relative numbers of male and female offspring in different 

 localities, at different times, with different ages of parents, and 

 so on. These statistics are valuable in proportion to the breadth 

 of their base, but it must be remarked that great care is necessary 

 in giving a physiological interpretation of statistical results. 



Cytological.. Some conclusions as to the determination of the 

 sex of the offspring have been based on observations of the germ- 

 cells in particular cases. Thus it has been shown that some 

 animals have two kinds of ova, the larger developing into females. 



