104 MAMMARY APPAEATUS OF THE MAMMAI.IA 



The genesis of these ridges was, according 

 to Profe, the result of an endeavour of the 

 organism to lay down in advance, by a single 

 process of differentiation, the material for the 

 formation of a series of homologous organs. 

 This developmental principle, he believed, was 

 of special importance just in the formation of 

 the mammary apparatus, because the ridge-like 

 form of the milk-line would prevent the dis- 

 placement of the nipples, the arrangement of 

 which in rows he regarded as necessary for the 

 preservation of the young, and therefore of the 

 species. 



This reasoning certainly sounds somewhat 

 plausible, but it will not hold. First of all it 

 is unintelligible how the arrangement of the 

 nipples in exact rows can tend to the preserva- 

 tion of the young, especially in view of the 

 fact that in the Marsupials practically all 

 possible arrangements occur from the serial to 

 the apparently completely circular. Further, 

 if the above-mentioned principle of develop- 

 ment, which, according to Prof6, is so im- 

 portant for the mammary apparatus, possessed 

 any actual value, its working should be observ- 

 able in thos^ marsupials furnished with rows 



