102 MAMMARY APPARATUS OF THE MAMMALIA 



regarded as pathological formations, resulting 

 from the dismemberment of milk ducts, or 

 from the displacement or splitting or doubling 

 of the primordia of the mammas. 



But much as the discovery of the milk-line 

 contributed to an increased understanding of 

 the mammary apparatus of the Placentals them- 

 selves, it introduced at the same time a great 

 difficulty from the point of view of phylogeny. 

 For now, naturally, arose the question. What is 

 the meanina: of the milk-line ? Hitherto all 

 attempts to answer this question have proved 

 unsatisfactory. It is obvious that it is not 

 possible to trace back the milk-line to the 

 lateral line of fishes or Urodela, and to the 

 glandular structures connected therewith, and 

 Wiedersheim, though he at one time accepted 

 this idea, following O. Schultze, soon dropped 

 it. Klaatsch and I met with just as little 

 success in attempting to discover the starting- 

 point of the milk-line in Marsupials. Klaatsch 

 believed he could explain the milk-lines as 

 rudiments of the pouch folds. He started 

 from the supposition, which we now know to 

 be false, that the marsupium arose through the 

 fusion of the nipple or mammary pouches. 



