106 SEX INHERITANCE 



aphids, one stem-mother may produce both Hnes; 

 i.e., some of her offspring may ultimately give rise 

 to sexual females and others to males. 



The Sex of Individuals Produced by 

 Artificial Parthenogenesis 



In only two species have individuals that have 

 been produced by artificial fertilization been raised 

 to a stage when their sex can be determined. Delage 

 reared two such sea urchins, that were probably 

 both males. Loeb has reared a number of frogs 

 that were mostly males, but a few were females. 

 Both sexes in Loeb's case appeared to have the 

 diploid number of chromosomes; but until more is 

 known of the chromosome situation in these cases 

 it is not possible to offer any probable explanation 

 of them. The work of Schmitt-Marcel and others 

 also throws some doubt on the possibility of accu- 

 rately determining the sex of frogs until long after 

 metamorphosis. 



Sex and Secondary Sexual Characters 



Males differ from females not only in the gonads 

 and in the accessory organs of reproduction (ducts, 

 glands, copulatory organs) but often show more 

 superficial differences that are called secondary 

 sexual characters. Genes concerned in the differ- 

 entiation of these have been shown, in two races 

 at least, not to lie in the sex-chromosomes. These 



