52 MAMMARY APPARATUS OF THE MAMMALIA 



Placentalia, and consequently differ very mucli 

 from those of the Monotremes. 



"What, now, have been the prevailing ideas 

 as to these conditions, when viewed in the light 

 of phylogenesis ? The answer to this question 

 is supplied by the famous so-called mammary- 

 pouch theory of Gegenbaur and Klaatsch. To 

 begin with, on the strength of the afore- 

 mentioned investigations of Morgan, Gegen- 

 baur, in 1876, believed that the nipples of the 

 Marsupialia could be derived from the mam- 

 mary pouches of Echidna. The nipple-pouches, 

 in his view, corresponded directly to the 

 mammary pouches, and their eversion, he 

 held, was produced as the result of adaptation 

 to the mouth of the suckling young. Gegen- 

 baur was confirmed in this view by observing 

 that the nipples of the Marsupialia first appear 

 as solid, knob-like, epidermal buds, growing 

 into the cutis, and he therefore called them 

 mammary-pouch primordia. The same buds 

 had been observed some years before (1873) by 

 his pupil Huss in the Placentalia. 



The assertion of Rein, directed against this 

 hypothesis, that Gegenbaur's supposed mam- 

 mary-pouch primordia were actually the first 



