112 MAMMARY APPARATUS OF THE MAMMALIA 



so-called areola mammae. The nipples of the 

 Carnivora represent a third type, the nipple 

 jiouch here being early reduced, and forming 

 only the tip of the nipple. The greater part 

 of the latter was held to be formed by the 

 cutis wall. Finally, a fourth type of nipple 

 was said to be characteristic of the Ruminants. 

 Here the nipple pouches were regarded as 

 persisting in their original condition without 

 eversion or reduction — as so-called " Strich- 

 kanale " — in the interior of the nipples, here 

 derived exclusively from the cutis wall. 



It is evident at once, assuming these views 

 to be correct, that the nipples of the Placentalia, 

 in spite of their external similarity, must 

 represent totall}^ heterogeneous formations, 

 Avhich could only have sprung from the nipples 

 of the Marsupials along different lines. The 

 mammary pouch of Echidna was to have served 

 " as a common starting-point, as a condition of 

 perfect indifference " (Klaatsch, 1884, p. 378). 



We see here, again, how much the unfor- 

 tunate mammary-pouch theory has influenced 

 the views of the scientific world. For, in spite 

 of the fact that the observations of Gegenbaur 

 and his pupils have repeatedly been shown to 



