DETERMINATION OF SEX. 869 



fertilization before menstruation favoring male births, after men- 

 struation female births; that it depends upon the nutritive con- 

 ditions of the ovum during development or of the maternal parent ; 

 that it depends upon the relative ages of the parents; that there 

 are preformed male and female ova and male and female sper- 

 matozoa, etc. What we may call the scientific study of the problem 

 began with the collection of statistics of births. Statistics in Europe 

 of 5,935,000 births indicate that 106 male children are born to 

 100 female, and the data from other countries show the same 

 fact of an excess of male children. Examination of these statistics 

 with reference to determining conditions led to the formulation 

 of the so-called Hofacker-Sadler law or laws, which may be stated 

 as follows: (1) When the man is older than the woman the ratio 

 of male births is increased (113 to 100). (2) When the parents are 

 of equal age the ratio of female births is increased (93.5 males to 

 100 females). (3) When the woman is older the ratio of female 

 births is still further increased (88.2 to 100). These laws have 

 been corroborated by some statisticians and contradicted or modi- 

 fied by others. Ploss attempted to show that poor nutritive con- 

 ditions affecting the parents, especially the mother, favor the 

 birth of boys. Dusing combined these results in a sort of general 

 compensatory law of nature, according to which a deficiency in 

 either sex leads, by a process of natural selection, to an increase 

 in the births of the opposite sex. Thus, when males are few in 

 number, as the result, for instance, of wars, females marry 

 later, and according to the Hofacker-Sadler law more males are 

 produced. When males are in excess early marriages are the rule 

 and this condition favors an excess of female births. However 

 interesting these statistics may be, it is very evident that they 

 do not touch the real problem of the cause of the determination 

 of sex. 



Modern work has turned largely to observations and direct 

 experiments upon the lower animals, particularly the inverte- 

 brates, with the result that a very large number of facts have 

 been collected of a most interesting kind, but difficult as yet to 

 interpret so as to formulate a general law. The trend of modern 

 work, however, tends to oppose an older view founded largely 

 upon experiments on frogs, bees, and wasps, according to which 

 the sex is not determined at or before fertilization, but is con- 

 trolled or may be controlled by the conditions of nourishment 

 during development, favorable conditions of nutriment leading 

 to the development of female cells from the germinal epithelium 

 of the embryo. The general opinion at present seems to be that 

 the sex of the embryo is determined in the egg before fertilization 

 or at the time of fertilization. This view assumes substantially 



