SUCCESSION OF MAMMALIAN TEETH. 445 



dentition succeeded by a permanent set of prismatic teeth. 

 This, I think, is not the natural explanation of his own 

 facts. He depicts five incisors on either side, above and 

 below, but of the upper ones two are small and calcified 

 and obviously from his figure represent the same tooth in two 

 generations, this is 13 or 4, so we see that one incisor has been 

 lost from the upper jaw, probably 13, the remaining three in- 

 cisors represent those of the typical diprotodonts of which No. 

 1 probably is the persistent tooth; below we have five in- 

 cisors, ii, 2 and 4 being vestigial and calcified, while 13 and 5 

 are well developed, the former persisting in the adult. 

 There is not the slightest reason for supposing that these 

 larger teeth are not true milk teeth. This explanation 

 brings the wombat into harmony with the other marsupials 

 and especially the macropididce. 



The third important contributor is Leche (34) and his 

 work covers a wider range among the mammalia. While 

 agreeing with the last two authors in the main, he believes 

 that the milk dentition is in every respect older than the 

 replacing one. His researches in the marsupials include a 

 most interesting and new discovery in Myrmecobius of a 

 number of small calcified teeth representing an earlier den- 

 tition than the milk set. This I have verified myself in the 

 genus named and probably also in Phascologale ; in order to 

 distinguish the series from the milk set I shall for the pre- 

 sent speak of it as the premilk dentition. This discovery 

 relegates the milk dentition to a second and the replacing 

 teeth of the higher mammals to a third generation of teeth. 



The animal of whose dentition Leche has published the 

 most detailed account is the hedgehog, in which he has dis- 

 covered a very curious condition, for it appears that quite a 

 number of the milk teeth persist in the adult dentition, viz. : — 



di3, dpm2, m 1-3 

 di3, dc, dpm3, m 1-3. 



This, if true, would rather strengthen the time-honoured 

 view that the insectivora are very primitive mammals. 



Both Leche (34) and Kukenthal (35) in the seal, and 

 Rose (31) in man, have come to the conclusion that there 



