8 MAMMARY APPARATUS OF THE MAMMALIA 



possession of these peculiar mammary organs. 

 This is a question which has given rise to 

 much discussion. To begin with, it may be 

 emphasized that up till now it has not been 

 possible to bring the mammary apparatus 

 into connection with any organs of the lower 

 vertebrates from which they could be derived, 

 as is the case with the other characteristics 

 of the Mammals. Leaving aside some vague 

 suggestions, it has been generally held that 

 the mammary apparatus arose as an entirely 

 new formation in the first Mammals. But 

 why should the sweat glands on two particular 

 spots of the abdominal wall — and there only 

 — have developed into milk glands ? To 

 this question there can be but one answer 

 already indicated by Darwin in his " Origin 

 of Species " : On those particular spots there 

 must have existed specially intimate relations 

 between the mother and the young, which 

 conditioned the development therefrom of 

 the mammary apparatus. Darwin suggested 

 that these relations were rendered possible 

 by the presence of a marsupium. 



The researches of Gegenbaur seemingly 

 confirmed this hypothesis, and since then 



