THE MILK-LINE 103 



Naturally the conclusion drawn from this false 

 supposition was untenable. I then suggested 

 the derivation of the milk-line from the fusion 

 of the marsupial pockets, such fusion producing 

 in certain species solid epidermal ridges, as, for 

 example, is the case in Myrmecobius. But this 

 supposition could not be correct, because the 

 marsupial pockets (the suggested milk-lines) 

 succeed, in point of time, the nipple primordia, 

 whilst in the Placentals just the reverse holds 

 true, the milk lines appearing before the nipple 

 primordia. 



The difficulty of tracing any homologue of 

 the milk-line led other workers to do away 

 with the problem altogether, by simply denying 

 to the milk-line any phylogenetic significance 

 at all. Thus Beard, in 1898, explained the 

 milk-line as a mere " developmental structure, 

 which, first appearing as a distinct line or ridge, 

 afterwards becomes broken up into a number 

 of separate entities." Shortly afterwards Profe, 

 and more recently Brouha and Pinkus, following 

 Beard's suggestion, placed the milk-line in the 

 same category with the neural crest and the 

 dental lamina and other transitory epithelial 

 ridges only met with during embryonal develop- 

 xaent, 



