THE GENERATIVE GLANDS 357 



retained in the receptaculum seminis. From the eggs into which 

 the sperm cells penetrate, females that is queens and workers- 

 are hatched, while from the unfertilized eggs, males that is 

 drones proceed. Lenhossek thinks it possible that the sperm 

 cells find access only to those eggs which possess female charac- 

 teristics and that they do not penetrate the male eggs. 



These observations show that, in the low r er forms of life, 

 sex differentiation may already exist in the unfertilized egg, or 

 it may be determined in the course of, or immediately after, 

 fertilization. But it must not be imagined that these observations 

 apply indiscriminately to animals of the higher orders. On the 

 contrary, where these are concerned, we know neither the factor 

 which determines sex nor the moment at which sex is decided. 

 The fact that twins from one ovum which are probably the out- 

 come of division of the germ at a very early stage of segmenta- 

 tion are almost invariably of the same sex, suggests that the 

 determination of sex in man also takes place at a very early 

 developmental stage. 



This assumption is contradicted, however, by a large number 

 of facts. In the first place, the primordial beginning of the 

 body is, in all vertebrates, sexually indifferent. It is not until the 

 embryo has made considerable advancement at the fifth week in 

 man that a differentiation of the primitive genital trace into a 

 unisexual genital gland takes place. It may be that in vertebrates, 

 as well as in invertebrates, both male and female glands develop 

 simultaneously from the same primitive genital trace. As Pfliiger 

 showed in the case of Bufo cinereus, there is a developmental stage 

 of true hermaphroditism, which later passes off. Cases of herma- 

 phroditismus biglandularis are sometimes, though rarely, met 

 with in man ; these are individuals in which the generative glands 

 of both sexes are present either on one or both sides, or a female 

 gland on one side and a male gland on the other side. These 

 findings show that the sex of the individual is not determined 

 until a late stage of development, and that the differentiation of 

 the unisexual glands does not take place until after the develop- 

 ment of the undifferentiated sexual cells. 



If the specific generative gland is regarded as the charac- 

 teristic of sex, the body of the embryo must be regarded as 

 sexless as long as the primitive genital trace remains undif- 

 ferentiated. Such being the case we should be compelled lo 

 admit that the determining factor in the differentiation of sex is, 

 as far as our present knowledge goes, unknown. We simply do 

 not know why it is that, at a certain moment in the life of the 

 embryo, the primitive genital trace develops, in one instance into 

 a testis, in another into an ovary, and in certain very rare cases, 

 into both. 



But sexual dimorphism is not confined to dimorphism of the 

 cells of generation ; it extends to other bodily characteristics. 



