CHAPTER III 



^ ITE come now to the discussion of the 

 V V organization of the mammary appar- 

 atus in the highest order of Mammals — namely, 

 the riacentalia (Monodelphia, Eutheria). Its 

 relations are here very materially influenced 

 by the fact that owing to the lengthening 

 of the intra-uterine period of development the 

 young are born in a far more advanced state 

 than in the Marsupialia. In correlation there- 

 with marsupial pockets and marsupium are 

 absent, and the mammary apparatus consists 

 solely of the nipples and milk glands, the 

 latter being quite similar to those of the 

 Marsupials. 



The number and likewise the arrangement of 

 the nipples in the Placentalia varies still more 

 considerably than in the Marsupialia. The 

 maximum number of nipples — namely, twenty- 

 two — reached by the primitive insectivore 

 Centetes ecaudatus parallels that met with 



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