RELATIONS OF MARSUPIALS AND PLACENTALS 139 



independently in both groups. I need only 

 recall to you the names of these parts — gland 

 area and nipples, mammary glands and milk 

 glands, incubatorium and marsupium, sphincter 

 incubatorii and sphincter marsupii. A connec- 

 tion, then, between the Monotremes and Mar- 

 supials existed merely in so far as they are 

 derived from common ancestors — Huxley's 

 Prototheria. 



The relation between the Marsupials and 

 Placentals is of a similar kind. The parallel 

 development of the various nipple types 

 in both groups, and the absence of the 

 pouch in the Placentals as a primari/ feature, 

 point most decisively against a direct deriva- 

 tion of the Placentals from pouch -bearing 

 Marsupials. On the contrary, all the evidence 

 goes to show that these two orders arose 

 independently from their common ancestors — 

 Huxley's Metatheria. 



Thus a knowledge of the ontogeny of the 

 mammary apparatus confirms in the fullest way 

 the correctness of the phylogenetic conceptions 

 put forward by Huxley, with this one slight 

 modification perhaps, that the distinction 

 between the Eutheria as hypothetical racial 



