96 INFLUENCE OF HORMONES 



The Mammary or Milk Glands 



The milk glands in Mammals constitute one of the 

 most remarkable of secondary sexual characters. 

 Except in their functional relations to the primary 

 organs, the ovaries, and to the uterus, there is 

 nothing sexual about them. They are parts of the 

 skin, being nothing more or less than enormous 

 enlargements of dermal glands, either sebaceous 

 or sudoriparous. Uterine and mammary functions 

 are generally regarded as essentially female char- 

 acteristics, and are included in the popular idea of 

 the sex of woman. Scientifically, of course, they are 

 not at all necessary or universal features of the 

 female sex, but are peculiar to the mammalian class 

 of Vertebrates in which they have been evolved. 

 Milk glands, then, are somatic sex-characters common 

 to a whole class, instead of being restricted to a 

 family like the antlers in Cervidae. There is not 

 the slightest trace or rudiment of them in other 

 classes of Vertebrates, such as Birds or Reptiles. 

 They are not actually sexual in their nature, since 

 their function is to supply food for the young, not to 

 play a part in the relations of the sexes. What is 

 sexual about them is — firstly, that they are normally 

 fully developed only in the female, rudimentary in 

 the male; secondly, that their periodical develop- 

 ment and functional activity depends on the changes 

 which take place in the ovarj^ and uterus. Many 

 investigators have endeavoured to discover the 

 nature of the nexus between the latter organs and 

 the milk glands. 



That this nexus is of the nature of a hormone is 

 generally agreed, and may be regarded as having 



