president's address. 689 



vertical successor, and that the very tooth which has a vertical 

 successor in the case of the Marsupials of the present day. 



Rose* gives an account of the results of a study of the develop- 

 ment of the teeth in the Max'supials, in which he states that, as 

 regards the general mode of development, there is little difference 

 between that group and other Mammals. He finds that, as is 

 generally accepted, it is for the most part only the last premolar 

 that is formed from the accessory ridge ; that is to say, that tooth 

 alone belongs to what corresponds to the permanent set of other 

 Mammals ; but the same in all probability holds good of the last 

 incisors of Perameles as well as Macropus and Phalmigista. This 

 last premolar either simply pushes itself into a gap in the first row 

 of teeth — none of the lati.er becoming absorbed (as in Didelphys, 

 Plialangista Cookii, Ferameles Doreyanus, Belideus bidens, Myr- 

 mecobius), or takes the place of the last premolar of the first set 

 which becomes absorbed (Phalangista sp., Macropus lugens, M. 

 giganteus, Phascogale peiiicillata and the fossil Triacanthodon 

 serrida). 



With the exception of the last premolar, and pei'haps the last 

 incisors, the permanent teeth of the Marsupials seem, as pre- 

 viously pointed out by Kiibenthal, to be the equivalents not of the, 

 permanent teeth of other Mammals but of the milk or deciduous 

 set. 



Throughout the Vertebrate series, he points out, from the 

 Selachii to the Mammalia, there is a .tendency to the evolution of 

 the deatary system taking the direction of a reduction in the 

 number of rows and series and an advance in the specialisation of 

 the individual tooth. The Marsupials, in which the second den- 

 tition has been reduced almost to a vanishing point, thus appear 

 to have advanced beyond the placental Mammals on the former 

 of these lines of tooth evolution ; but this can hardly be regarded 

 as a higher development, since the loss of the second dentition can 

 only be looked upon as an advance when the teeth of the single 

 series grow throughout life from persistent pulps — a condition 



* "Ueberdie Zahnenentwickelung der Beutelthiere." 'Anat. Anzeiger, 

 1892.' 



