120 MAMMAEY APPARA'TUS OF THE MAMMALIA 



It is therefore evident that three out of the 

 four types of nipples recognized by Gegenbaur 

 and Klaatsch are to be interpreted in an entirely 

 different manner. In the Carnivora alone did 

 they correctly maintain that the original nipple 

 pouch is completely absorbed in the develop- 

 ment of the later nipple. In all other forms 

 they made the mistake of deriving from the 

 nipple pouches not only the nipples but also 

 accessory formations, such as the secondary 

 nipple sheath in the Murids;, the areola mammaj 

 in man, and the so-called " Strichkanal " in 

 Ruminants. There can be no question of all 

 this as we have seen. The secondary nipple 

 sheaths of mice and of the mole are not the 

 permanent nipple pouches, but are undoubtedly 

 new formations. The areola mammae of man, 

 and certainly also of the rest of Primates, has 

 nothing to do with the nipple pouch, but merely 

 represents a specially differentiated part of the 

 cutis wall around the mammilla, such as is 

 similarly found in numerous other Mammals, 

 particularly in Rodentia and Carnivora. The 

 " Strichkanal " of the Ruminants is really 

 nothing but a milk duct, whose strong develop- 

 ment is entirely due to compensatory growth. 



