142. Transactions of the Society. 



scientifically or not at all, the solutions suggested have not always 

 adhered strictly to scientific method. Scores of books and pamph- 

 lets redolent of good intentions must be set aside because ofobrious 

 scientific unsoundness. Some lay stress on what even the most 

 tolerant must call unverifiable factors, such as the desire of the 

 parent to have a male child ; others allege the operation of factors 

 which are physiologically absurd ; others base a generalization on 

 an outrageously small number of cases. The number of theories 

 on the subject is legion, and one can hardly wonder, since the 

 practical importance of the problem is as great as its theoretical 

 interest. 



The Problem Stated. 



2. The general problem is : What determines whether an 

 embryo will develop into a male or into a female organism ? But 

 let us look at some of the particular forms of the problem. 

 What are called " true twins " in the human race, which appear to 

 result from the division of a single ovum into two independently 

 developing ova, are always of the same sex ; but ordinary twins, 

 which result from two distinct ova developing simultaneously, are 

 often of different sexes. Why is there this difference ? 



In one household the family consists of both boys and girls ; 

 in the house next door to the right the children are all girls ; in 

 the house next door to the left the children are all boys ! What 

 determines this ? A guillemot usiially lays but one egg in a 

 season : what determines the sex of the offspring ? A setting of 

 hen's eggs gives rise to cocks and hens in varying proportions — is 

 the proportion practically modifiable ? The unfertilized eggs of a 

 queen-bee develop into drones ; the unfertilized eggs of aphides 

 develop into females all through the summer, but at the end of the 

 season males are produced. What does this mean ? In great part 

 the question comes to be, When is the sex of the offspring deter- 

 mined finally ? Is there sex-determination in ova before fertiliza- 

 tion, or during fertilization, or in the course of development after 

 fertilization ? How long may a germ-cell or an embryo remain 

 with the potentiality of either sex ? 



Three Chief Methods of Investigation. 



3. The problem has been attacked scientifically along three 

 distinct lines, and it is particularly interesting to notice that some 

 of the clearest steps of progress have been made by the co-opera- 

 tion of two methods. 



Statistical. — Some generalizations as to the determination of 

 the sex of the offspring have been based on statistics of the relative 

 numbers of male and female offspring in different localities, at 

 different times (e.g. in times of war and famine), with different ages 



